--- a/configure.in
+++ b/configure.in
@@ -1439,89 +1439,68 @@ if test "$GNU_CC"; then
                     DSO_LDOPTS="$DSO_LDOPTS -Wl,--warn-unresolved-symbols"
                 fi
                 ;;
             esac
         fi
     fi
 
     # Turn on gcc/clang warnings:
-    # https://gcc.gnu.org/onlinedocs/gcc-4.4.0/gcc/Warning-Options.html
-    #
-    # -Wall - turn on a lot of warnings
-    # -Wchar-subscripts - catches array index using signed char
-    # -Wcomment - catches nested comments
+    # https://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Warning-Options.html
+
+    # -Wall - lots of useful warnings
     # -Wempty-body - catches bugs, e.g. "if (c); foo();", few false positives
-    # -Wendif-labels - catches `#else FOO` and `#endif FOO` not in comment
-    # -Wenum-compare - catches comparison of different enum types
     # -Wignored-qualifiers - catches returns types with qualifiers like const
-    # -Wint-to-pointer-cast - catches cast to pointer from integer of different size
-    # -Wmultichar - catches multicharacter integer constants like 'THIS'
-    # -Wnon-literal-null-conversion - catches expressions used as a null pointer constant
-    # -Wnonnull - catches NULL used with functions arguments marked as non-null
     # -Wpointer-arith - catches pointer arithmetic using NULL or sizeof(void)
-    # -Wpointer-sign - catches mixing pointers to signed and unsigned types
-    # -Wpointer-to-int-cast - catches casts from pointer to different sized int
-    # -Wreturn-type - catches missing returns, zero false positives
-    # -Wsequence-point - catches undefined order behavior like `a = a++`
-    # -Wsign-compare - catches comparison of signed and unsigned types
-    # -Wtrigraphs - catches unlikely use of trigraphs
     # -Wtype-limits - catches overflow bugs, few false positives
-    # -Wunknown-pragmas - catches unexpected #pragma directives
-    #
     _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wall"
     _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wempty-body"
-    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wpointer-to-int-cast"
-    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wsign-compare"
+    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wignored-qualifiers"
+    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wpointer-arith"
     _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wtype-limits"
 
-    # Treat some warnings as errors if --enable-warnings-as-errors:
+    # -Wnon-literal-null-conversion - catches expressions used as a null pointer constant
+    # -Wsometimes-initialized - catches some uninitialized values
+    #
+    # XXX: at the time of writing, the version of clang used on the OS X test
+    # machines has a bug that causes it to reject some valid files if both
+    # -Wnon-literal-null-conversion and -Wsometimes-uninitialized are
+    # specified. We work around this by instead using
+    # -Werror=non-literal-null-conversion, but we only do that when
+    # --enable-warnings-as-errors is specified so that no unexpected fatal
+    # warnings are produced.
     if test "$MOZ_ENABLE_WARNINGS_AS_ERRORS"; then
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=char-subscripts"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=comment"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=endif-labels"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=enum-compare"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=ignored-qualifiers"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=int-to-pointer-cast"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=multichar"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=nonnull"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=pointer-arith"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=pointer-sign"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=return-type"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=sequence-point"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=trigraphs"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=uninitialized"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=unknown-pragmas"
-
-        MOZ_C_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_c_has_werror_non_literal_null_conversion)
-        MOZ_C_SUPPORTS_WARNING(-Werror=, sometimes-uninitialized, ac_c_has_sometimes_uninitialized)
-    fi
-
-    # Turn off the following warnings that -Wall turns on:
-    # -Wno-unused - lots of violations in third-party code
-    # -Wno-unused-local-typedef - catches unused typedefs, which are commonly used in assertion macros
-    #
-    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wno-unused"
-
-    MOZ_CXX_SUPPORTS_WARNING(-Wno-, unused-local-typedef, ac_cxx_has_wno_unused_local_typedef)
-
+        MOZ_C_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_c_has_non_literal_null_conversion)
+    fi
+    MOZ_C_SUPPORTS_WARNING(-W, sometimes-uninitialized, ac_c_has_sometimes_uninitialized)
+
+    # -Wcast-align - catches problems with cast alignment
     if test -z "$INTEL_CC" -a -z "$CLANG_CC"; then
        # Don't use -Wcast-align with ICC or clang
        case "$CPU_ARCH" in
            # And don't use it on hppa, ia64, sparc, arm, since it's noisy there
            hppa | ia64 | sparc | arm)
            ;;
            *)
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wcast-align"
            ;;
        esac
     fi
 
+    # Turn off some non-useful warnings that -Wall turns on.
+
+    # -Wno-unused - lots of violations in third-party code
+    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wno-unused"
+
+    # -Wno-unused-local-typedef - catches unused typedefs, which are commonly used in assertion macros
+    MOZ_C_SUPPORTS_WARNING(-Wno-, unused-local-typedef, ac_c_has_wno_unused_local_typedef)
+
     _DEFINES_CFLAGS='-include $(topobjdir)/mozilla-config.h -DMOZILLA_CLIENT'
     _USE_CPP_INCLUDE_FLAG=1
+
     ASFLAGS="$ASFLAGS $_DEFINES_CFLAGS"
 
 elif test "$SOLARIS_SUNPRO_CC"; then
     DSO_CFLAGS=''
     if test "$CPU_ARCH" = "sparc"; then
         # for Sun Studio on Solaris/SPARC
         DSO_PIC_CFLAGS='-xcode=pic32'
     else
@@ -1543,101 +1522,83 @@ else
     _DEFINES_CFLAGS='$(ACDEFINES) -D_MOZILLA_CONFIG_H_ -DMOZILLA_CLIENT'
 fi
 
 if test "$GNU_CXX"; then
     # FIXME: Let us build with strict aliasing. bug 414641.
     CXXFLAGS="$CXXFLAGS -fno-exceptions -fno-strict-aliasing"
 
     # Turn on gcc/clang warnings:
-    # https://gcc.gnu.org/onlinedocs/gcc-4.4.0/gcc/Warning-Options.html
-    #
-    # -Wall - turn on a lot of warnings
+    # https://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Warning-Options.html
+
+    # -Wall - lots of useful warnings
     # -Wempty-body - catches bugs, e.g. "if (c); foo();", few false positives
-    # -Wendif-labels - catches `#else FOO` and `#endif FOO` not in comment
-    # -Wint-to-pointer-cast - catches cast to pointer from integer of different size
-    # -Wmissing-braces - catches aggregate initializers missing nested braces
-    # -Wnon-literal-null-conversion - catches expressions used as a null pointer constant
     # -Woverloaded-virtual - function declaration hides virtual function from base class
-    # -Wparentheses - catches `if (a=b)` and operator precedence bugs
     # -Wpointer-arith - catches pointer arithmetic using NULL or sizeof(void)
-    # -Wrange-loop-analysis - catches copies during range-based for loops.
-    # -Wreturn-type - catches missing returns, zero false positives
-    # -Wsequence-point - catches undefined order behavior like `a = a++`
-    # -Wsign-compare - catches comparison of signed and unsigned types
-    # -Wswitch - catches switches without all enum cases or default case
-    # -Wtrigraphs - catches unlikely use of trigraphs
     # -Wtype-limits - catches overflow bugs, few false positives
-    # -Wunused-label - catches unused goto labels
-    # -Wwrite-strings - catches non-const char* pointers to string literals
-    #
     _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wall"
     _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wempty-body"
     _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Woverloaded-virtual"
-    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wsign-compare"
-    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wwrite-strings"
-
-    # Treat some warnings as errors if --enable-warnings-as-errors:
+    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wpointer-arith"
+    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wtype-limits"
+
+    # -Wnon-literal-null-conversion - catches expressions used as a null pointer constant
+    # -Wrange-loop-analysis - catches copies during range-based for loops.
+    # -Wsometimes-initialized - catches some uninitialized values
+    #
+    # XXX: at the time of writing, the version of clang used on the OS X test
+    # machines has a bug that causes it to reject some valid files if both
+    # -Wnon-literal-null-conversion and -Wsometimes-uninitialized are
+    # specified. We work around this by instead using
+    # -Werror=non-literal-null-conversion, but we only do that when
+    # --enable-warnings-as-errors is specified so that no unexpected fatal
+    # warnings are produced.
     if test "$MOZ_ENABLE_WARNINGS_AS_ERRORS"; then
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=endif-labels"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=int-to-pointer-cast"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=missing-braces"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=parentheses"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=pointer-arith"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=return-type"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=sequence-point"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=switch"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=trigraphs"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=type-limits"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=uninitialized"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=unused-label"
-
-        MOZ_CXX_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_cxx_has_werror_non_literal_null_conversion)
-        MOZ_CXX_SUPPORTS_WARNING(-Werror=, range-loop-analysis, ac_cxx_has_range_loop_analysis)
-        MOZ_CXX_SUPPORTS_WARNING(-Werror=, sometimes-uninitialized, ac_cxx_has_sometimes_uninitialized)
-    fi
-
-    # Turn off the following warnings that -Wall turns on:
-    # -Wno-invalid-offsetof - we use offsetof on non-POD types frequently
-    # -Wno-inline-new-delete - we inline 'new' and 'delete' in mozalloc
-    # -Wno-unused-local-typedef - catches unused typedefs, which are commonly used in assertion macros
-    #   for performance reasons, and because GCC and clang accept it (though
-    #   clang warns about it).
-    #
-    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wno-invalid-offsetof"
-
-    MOZ_CXX_SUPPORTS_WARNING(-Wno-, inline-new-delete, ac_cxx_has_wno_inline_new_delete)
-    MOZ_CXX_SUPPORTS_WARNING(-Wno-, unused-local-typedef, ac_cxx_has_wno_unused_local_typedef)
-
+        MOZ_CXX_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_cxx_has_non_literal_null_conversion)
+    fi
+    MOZ_CXX_SUPPORTS_WARNING(-W, range-loop-analysis, ac_cxx_has_range_loop_analysis)
+    MOZ_CXX_SUPPORTS_WARNING(-W, sometimes-uninitialized, ac_cxx_has_sometimes_uninitialized)
+
+    # -Wcast-align - catches problems with cast alignment
     if test -z "$INTEL_CXX" -a -z "$CLANG_CXX"; then
        # Don't use -Wcast-align with ICC or clang
        case "$CPU_ARCH" in
            # And don't use it on hppa, ia64, sparc, arm, since it's noisy there
            hppa | ia64 | sparc | arm)
            ;;
            *)
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wcast-align"
            ;;
        esac
     fi
 
-    _DEFINES_CXXFLAGS='-DMOZILLA_CLIENT -include $(topobjdir)/mozilla-config.h'
-    _USE_CPP_INCLUDE_FLAG=1
+    # Turn off some non-useful warnings that -Wall turns on.
+
+    # -Wno-invalid-offsetof - we use offsetof on non-POD types frequently
+    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wno-invalid-offsetof"
+
+    # -Wno-inline-new-delete - we inline 'new' and 'delete' in mozalloc
+    # -Wno-unused-local-typedef - catches unused typedefs, which are commonly used in assertion macros
+    MOZ_CXX_SUPPORTS_WARNING(-Wno-, inline-new-delete, ac_cxx_has_wno_inline_new_delete)
+    MOZ_CXX_SUPPORTS_WARNING(-Wno-, unused-local-typedef, ac_cxx_has_wno_unused_local_typedef)
 
     # Recent clang and gcc support C++11 deleted functions without warnings if
     # compiling with -std=c++0x or -std=gnu++0x (or c++11 or gnu++11 in very new
     # versions).  We can't use -std=c++0x yet, so gcc's support must remain
     # unused.  But clang's warning can be disabled, so when compiling with clang
     # we use it to opt out of the warning, enabling (macro-encapsulated) use of
     # deleted function syntax.
     if test "$CLANG_CXX"; then
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wno-c++0x-extensions"
         MOZ_CXX_SUPPORTS_WARNING(-Wno-, extended-offsetof, ac_cxx_has_wno_extended_offsetof)
     fi
 
+    _DEFINES_CXXFLAGS='-DMOZILLA_CLIENT -include $(topobjdir)/mozilla-config.h'
+    _USE_CPP_INCLUDE_FLAG=1
+
 else
     _DEFINES_CXXFLAGS='-DMOZILLA_CLIENT -D_MOZILLA_CONFIG_H_ $(ACDEFINES)'
 fi
 
 dnl ========================================================
 dnl Checking for 64-bit OS
 dnl ========================================================
 if test "$COMPILE_ENVIRONMENT"; then

--- a/js/src/configure.in
+++ b/js/src/configure.in
@@ -1182,101 +1182,65 @@ if test "$GNU_CC"; then
     _SAVE_LDFLAGS=$LDFLAGS
     LDFLAGS="$LDFLAGS -Wl,--build-id"
     AC_TRY_LINK(,,AC_MSG_RESULT([yes])
                   [NSPR_LDFLAGS="$NSPR_LDFLAGS -Wl,--build-id"],
                   AC_MSG_RESULT([no])
                   LDFLAGS=$_SAVE_LDFLAGS)
 
     # Turn on gcc/clang warnings:
-    # https://gcc.gnu.org/onlinedocs/gcc-4.4.0/gcc/Warning-Options.html
-    #
-    # -Wall - turn on a lot of warnings
-    # -Waddress - catches suspicious uses of memory addresses
-    # -Wchar-subscripts - catches array index using signed char
-    # -Wcomment - catches nested comments
+    # https://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Warning-Options.html
+
+    # -Wall - lots of useful warnings
     # -Wempty-body - catches bugs, e.g. "if (c); foo();", few false positives
-    # -Wendif-labels - catches `#else FOO` and `#endif FOO` not in comment
-    # -Wenum-compare - catches comparison of different enum types
     # -Wignored-qualifiers - catches returns types with qualifiers like const
-    # -Wimplicit-function-declaration - catches missing C function prototypes
-    # -Wint-to-pointer-cast - catches cast to pointer from integer of different size
-    # -Wmissing-braces - catches aggregate initializers missing nested braces
-    # -Wmultichar - catches multicharacter integer constants like 'THIS'
+    # -Wpointer-arith - catches pointer arithmetic using NULL or sizeof(void)
+    # -Wtype-limits - catches overflow bugs, few false positives
+    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wall"
+    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wempty-body"
+    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wignored-qualifiers"
+    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wpointer-arith"
+    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wtype-limits"
+
     # -Wnon-literal-null-conversion - catches expressions used as a null pointer constant
-    # -Wnonnull - catches NULL used with functions arguments marked as non-null
-    # -Wparentheses - catches `if (a=b)` and operator precedence bugs
-    # -Wpointer-arith - catches pointer arithmetic using NULL or sizeof(void)
-    # -Wpointer-sign - catches mixing pointers to signed and unsigned types
-    # -Wpointer-to-int-cast - catches casts from pointer to different sized int
-    # -Wreturn-type - catches missing returns, zero false positives
-    # -Wsequence-point - catches undefined order behavior like `a = a++`
-    # -Wsign-compare - catches comparison of signed and unsigned types
-    # -Wswitch - catches switches without all enum cases or default case
-    # -Wtrigraphs - catches unlikely use of trigraphs
-    # -Wtype-limits - catches overflow bugs, few false positives
-    # -Wunknown-pragmas - catches unexpected #pragma directives
-    # -Wwrite-strings - catches non-const char* pointers to string literals
+    # -Wsometimes-initialized - catches some uninitialized values
     #
-    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wall"
-    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wsign-compare"
-    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wtype-limits"
-
-    # Treat some warnings as errors if --enable-warnings-as-errors:
+    # XXX: at the time of writing, the version of clang used on the OS X test
+    # machines has a bug that causes it to reject some valid files if both
+    # -Wnon-literal-null-conversion and -Wsometimes-uninitialized are
+    # specified. We work around this by instead using
+    # -Werror=non-literal-null-conversion, but we only do that when
+    # --enable-warnings-as-errors is specified so that no unexpected fatal
+    # warnings are produced.
     if test "$MOZ_ENABLE_WARNINGS_AS_ERRORS"; then
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=address"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=char-subscripts"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=comment"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=empty-body"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=endif-labels"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=enum-compare"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=ignored-qualifiers"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=implicit-function-declaration"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=int-to-pointer-cast"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=missing-braces"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=multichar"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=nonnull"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=parentheses"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=pointer-arith"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=pointer-sign"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=pointer-to-int-cast"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=return-type"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=sequence-point"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=switch"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=trigraphs"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=uninitialized"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=unknown-pragmas"
-        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=write-strings"
-
-        MOZ_C_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_c_has_werror_non_literal_null_conversion)
-        MOZ_C_SUPPORTS_WARNING(-Werror=, sometimes-uninitialized, ac_c_has_sometimes_uninitialized)
+        MOZ_C_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_c_has_non_literal_null_conversion)
     fi
-
-    # Turn off the following warnings that -Wall turns on:
-    # -Wno-unused - lots of violations in third-party code
-    # -Wno-inline-new-delete - we inline 'new' and 'delete' in mozalloc
-    # -Wno-unused-local-typedef - catches unused typedefs, which are commonly used in assertion macros
-    #
-    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wno-unused"
-
-    MOZ_CXX_SUPPORTS_WARNING(-Wno-, inline-new-delete, ac_cxx_has_wno_inline_new_delete)
-    MOZ_CXX_SUPPORTS_WARNING(-Wno-, unused-local-typedef, ac_cxx_has_wno_unused_local_typedef)
-
+    MOZ_C_SUPPORTS_WARNING(-W, sometimes-uninitialized, ac_c_has_sometimes_uninitialized)
+
+    # -Wcast-align - catches problems with cast alignment
     if test -z "$INTEL_CC" -a -z "$CLANG_CC"; then
        # Don't use -Wcast-align with ICC or clang
        case "$CPU_ARCH" in
            # And don't use it on hppa, ia64, sparc, arm, since it's noisy there
            hppa | ia64 | sparc | arm)
            ;;
            *)
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wcast-align"
            ;;
        esac
     fi
 
+    # Turn off some non-useful warnings that -Wall turns on.
+
+    # -Wno-unused - lots of violations in third-party code
+    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wno-unused"
+
+    # -Wno-unused-local-typedef - catches unused typedefs, which are commonly used in assertion macros
+    MOZ_C_SUPPORTS_WARNING(-Wno-, unused-local-typedef, ac_c_has_wno_unused_local_typedef)
+
     _DEFINES_CFLAGS='-include $(topobjdir)/js/src/js-confdefs.h -DMOZILLA_CLIENT'
     _USE_CPP_INCLUDE_FLAG=1
 
 elif test "$SOLARIS_SUNPRO_CC"; then
     DSO_CFLAGS=''
     if test "$CPU_ARCH" = "sparc"; then
         # for Sun Studio on Solaris/SPARC
         DSO_PIC_CFLAGS='-xcode=pic32'
@@ -1296,113 +1260,86 @@ else
 
     DSO_CFLAGS=''
     DSO_PIC_CFLAGS='-KPIC'
     _DEFINES_CFLAGS='$(ACDEFINES) -D_JS_CONFDEFS_H_ -DMOZILLA_CLIENT'
 fi
 
 if test "$GNU_CXX"; then
     # Turn on gcc/clang warnings:
-    # https://gcc.gnu.org/onlinedocs/gcc-4.4.0/gcc/Warning-Options.html
-    #
-    # -Wall - turn on a lot of warnings
-    # -Wchar-subscripts - catches array index using signed char
-    # -Wcomment - catches nested comments
-    # -Wconversion-null - catches conversions between NULL and non-pointer types
+    # https://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Warning-Options.html
+
+    # -Wall - lots of useful warnings
     # -Wempty-body - catches bugs, e.g. "if (c); foo();", few false positives
-    # -Wendif-labels - catches `#else FOO` and `#endif FOO` not in comment
-    # -Wignored-qualifiers - catches returns types with qualifiers like const
-    # -Wint-to-pointer-cast - catches cast to pointer from integer of different size
-    # -Wmissing-braces - catches aggregate initializers missing nested braces
+    # -Woverloaded-virtual - function declaration hides virtual function from base class
+    # -Wpointer-arith - catches pointer arithmetic using NULL or sizeof(void)
+    # -Wtype-limits - catches overflow bugs, few false positives
+    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wall"
+    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wempty-body"
+    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Woverloaded-virtual"
+    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wpointer-arith"
+    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wtype-limits"
+
+    # -Wclass-varargs - ???
     # -Wnon-literal-null-conversion - catches expressions used as a null pointer constant
-    # -Woverloaded-virtual - function declaration hides virtual function from base class
-    # -Wparentheses - catches `if (a=b)` and operator precedence bugs
-    # -Wpointer-arith - catches pointer arithmetic using NULL or sizeof(void)
-    # -Wpointer-to-int-cast - catches casts from pointer to different sized int
     # -Wrange-loop-analysis - catches copies during range-based for loops.
-    # -Wreorder - catches ctor initializer list not matching class definition order
-    # -Wreturn-type - catches missing returns, zero false positives
-    # -Wsequence-point - catches undefined order behavior like `a = a++`
-    # -Wsign-compare - catches comparison of signed and unsigned types
-    # -Wswitch - catches switches without all enum cases or default case
-    # -Wtrigraphs - catches unlikely use of trigraphs
-    # -Wtype-limits - catches overflow bugs, few false positives
-    # -Wunknown-pragmas - catches unexpected #pragma directives
-    # -Wunused-label - catches unused goto labels
-    # -Wunused-value - catches unused expression results
-    # -Wwrite-strings - catches non-const char* pointers to string literals
+    # -Wsometimes-initialized - catches some uninitialized values
     #
-    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wall"
-    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wsign-compare"
-    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wtype-limits"
-
+    # XXX: at the time of writing, the version of clang used on the OS X test
+    # machines has a bug that causes it to reject some valid files if both
+    # -Wnon-literal-null-conversion and -Wsometimes-uninitialized are
+    # specified. We work around this by instead using
+    # -Werror=non-literal-null-conversion, but we only do that when
+    # --enable-warnings-as-errors is specified so that no unexpected fatal
+    # warnings are produced.
     MOZ_CXX_SUPPORTS_WARNING(-W, class-varargs, ac_cxx_has_wclass_varargs)
 
-    # Treat some warnings as errors if --enable-warnings-as-errors:
     if test "$MOZ_ENABLE_WARNINGS_AS_ERRORS"; then
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=char-subscripts"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=comment"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=endif-labels"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=ignored-qualifiers"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=int-to-pointer-cast"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=missing-braces"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=overloaded-virtual"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=parentheses"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=pointer-arith"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=reorder"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=return-type"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=sequence-point"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=switch"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=trigraphs"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=uninitialized"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=unknown-pragmas"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=unused-label"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=unused-value"
-        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=write-strings"
-
-        MOZ_CXX_SUPPORTS_WARNING(-Werror=, conversion-null, ac_cxx_has_werror_conversion_null)
-        MOZ_CXX_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_cxx_has_werror_non_literal_null_conversion)
-        MOZ_CXX_SUPPORTS_WARNING(-Werror=, range-loop-analysis, ac_cxx_has_range_loop_analysis)
-        MOZ_CXX_SUPPORTS_WARNING(-Werror=, sometimes-uninitialized, ac_cxx_has_sometimes_uninitialized)
+        MOZ_CXX_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_cxx_has_non_literal_null_conversion)
     fi
-
-    # Turn off the following warnings that -Wall turns on:
-    # -Wno-invalid-offsetof - we use offsetof on non-POD types frequently
-    # -Wno-unused-local-typedef - catches unused typedefs, which are commonly used in assertion macros
-    #
-    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wno-invalid-offsetof"
-
-    MOZ_CXX_SUPPORTS_WARNING(-Wno-, unused-local-typedef, ac_cxx_has_wno_unused_local_typedef)
-
+    MOZ_CXX_SUPPORTS_WARNING(-W, range-loop-analysis, ac_cxx_has_range_loop_analysis)
+    MOZ_CXX_SUPPORTS_WARNING(-W, sometimes-uninitialized, ac_cxx_has_sometimes_uninitialized)
+
+    # -Wcast-align - catches problems with cast alignment
     if test -z "$INTEL_CXX" -a -z "$CLANG_CXX"; then
        # Don't use -Wcast-align with ICC or clang
        case "$CPU_ARCH" in
            # And don't use it on hppa, ia64, sparc, arm, since it's noisy there
            hppa | ia64 | sparc | arm)
            ;;
            *)
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wcast-align"
            ;;
        esac
     fi
 
-    _DEFINES_CXXFLAGS='-DMOZILLA_CLIENT -include $(topobjdir)/js/src/js-confdefs.h'
-    _USE_CPP_INCLUDE_FLAG=1
+    # Turn off some non-useful warnings that -Wall turns on.
+
+    # -Wno-invalid-offsetof - we use offsetof on non-POD types frequently
+    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wno-invalid-offsetof"
+
+    # -Wno-inline-new-delete - we inline 'new' and 'delete' in mozalloc
+    # -Wno-unused-local-typedef - catches unused typedefs, which are commonly used in assertion macros
+    MOZ_CXX_SUPPORTS_WARNING(-Wno-, inline-new-delete, ac_cxx_has_wno_inline_new_delete)
+    MOZ_CXX_SUPPORTS_WARNING(-Wno-, unused-local-typedef, ac_cxx_has_wno_unused_local_typedef)
 
     # Recent clang and gcc support C++11 deleted functions without warnings if
     # compiling with -std=c++0x or -std=gnu++0x (or c++11 or gnu++11 in very new
     # versions).  We can't use -std=c++0x yet, so gcc's support must remain
     # unused.  But clang's warning can be disabled, so when compiling with clang
     # we use it to opt out of the warning, enabling (macro-encapsulated) use of
     # deleted function syntax.
     if test "$CLANG_CXX"; then
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Wno-c++0x-extensions"
         MOZ_CXX_SUPPORTS_WARNING(-Wno-, extended-offsetof, ac_cxx_has_wno_extended_offsetof)
     fi
 
+    _DEFINES_CXXFLAGS='-DMOZILLA_CLIENT -include $(topobjdir)/js/src/js-confdefs.h'
+    _USE_CPP_INCLUDE_FLAG=1
+
 else
     _DEFINES_CXXFLAGS='-DMOZILLA_CLIENT -D_JS_CONFDEFS_H_ $(ACDEFINES)'
 fi
 
 dnl ========================================================
 dnl Checking for 64-bit OS
 dnl ========================================================
 if test "$COMPILE_ENVIRONMENT"; then