--- a/build/check-sync-exceptions
+++ b/build/check-sync-exceptions
@@ -10,8 +10,13 @@ configobj.py
 *~
 .#*
 #*#
 *.orig
 *.rej
 
 # Ignore "compiled" python files
 *.pyc
+
+# Disable Stylo - Bug 1380171
+# Until we can depend on taskcluster toolchain dependencies,
+# we don't have a good way to access LLVM.
+mozconfig.stylo

--- a/build/mozconfig.stylo
+++ b/build/mozconfig.stylo
@@ -1,2 +1,3 @@
-# Tell the build system where to find llvm-config for builds on automation.
-export LLVM_CONFIG="${TOOLTOOL_DIR:-$topsrcdir}/clang/bin/llvm-config"
+# Disable stylo.
+# https://bugzilla.mozilla.org/show_bug.cgi?id=1380171
+ac_add_options --disable-stylo

--- a/mail/config/mozconfigs/linux32/debug
+++ b/mail/config/mozconfigs/linux32/debug
@@ -2,16 +2,17 @@
 # of libX11 version > 1.4.99.1 (see bug 1350011).
 ac_add_options --disable-webrender
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-debug
 ac_add_options --enable-calendar
 
 . $topsrcdir/build/unix/mozconfig.linux32
+. "$topsrcdir/build/mozconfig.stylo"
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
 # Disable checking that add-ons are signed by the trusted root

--- a/mail/config/mozconfigs/linux32/nightly
+++ b/mail/config/mozconfigs/linux32/nightly
@@ -1,9 +1,10 @@
 . $topsrcdir/build/unix/mozconfig.linux32
+. "$topsrcdir/build/mozconfig.stylo"
 
 # Disable webrender on Linux buildbot builders to avoid the Rust requirement
 # of libX11 version > 1.4.99.1 (see bug 1350011).
 ac_add_options --disable-webrender
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --enable-profiling

--- a/mail/config/mozconfigs/linux32/release
+++ b/mail/config/mozconfigs/linux32/release
@@ -1,9 +1,10 @@
 . $topsrcdir/build/unix/mozconfig.linux32
+. "$topsrcdir/build/mozconfig.stylo"
 
 # Disable webrender on Linux buildbot builders to avoid the Rust requirement
 # of libX11 version > 1.4.99.1 (see bug 1350011).
 ac_add_options --disable-webrender
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --enable-official-branding

--- a/mail/config/mozconfigs/linux64/debug
+++ b/mail/config/mozconfigs/linux64/debug
@@ -2,16 +2,17 @@
 # of libX11 version > 1.4.99.1 (see bug 1350011).
 ac_add_options --disable-webrender
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-debug
 ac_add_options --enable-calendar
 
 . $topsrcdir/build/unix/mozconfig.linux
+. "$topsrcdir/build/mozconfig.stylo"
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
 # Disable checking that add-ons are signed by the trusted root

--- a/mail/config/mozconfigs/linux64/l10n-mozconfig
+++ b/mail/config/mozconfigs/linux64/l10n-mozconfig
@@ -1,9 +1,10 @@
 . $topsrcdir/build/unix/mozconfig.linux
+. "$topsrcdir/build/mozconfig.stylo"
 
 # Disable webrender on Linux buildbot builders to avoid the Rust requirement
 # of libX11 version > 1.4.99.1 (see bug 1350011).
 ac_add_options --disable-webrender
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --with-l10n-base=../../l10n

--- a/mail/config/mozconfigs/linux64/nightly
+++ b/mail/config/mozconfigs/linux64/nightly
@@ -1,9 +1,10 @@
 . $topsrcdir/build/unix/mozconfig.linux
+. "$topsrcdir/build/mozconfig.stylo"
 
 # Disable webrender on Linux buildbot builders to avoid the Rust requirement
 # of libX11 version > 1.4.99.1 (see bug 1350011).
 ac_add_options --disable-webrender
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --enable-profiling

--- a/mail/config/mozconfigs/linux64/release
+++ b/mail/config/mozconfigs/linux64/release
@@ -1,9 +1,10 @@
 . $topsrcdir/build/unix/mozconfig.linux
+. "$topsrcdir/build/mozconfig.stylo"
 
 # Disable webrender on Linux buildbot builders to avoid the Rust requirement
 # of libX11 version > 1.4.99.1 (see bug 1350011).
 ac_add_options --disable-webrender
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --enable-official-branding

--- a/mail/config/mozconfigs/macosx64/debug
+++ b/mail/config/mozconfigs/macosx64/debug
@@ -21,14 +21,8 @@ export MOZ_PACKAGE_JSSHELL=1
 ac_add_options --with-ccache
 
 # Run client.py
 mk_add_options CLIENT_PY_ARGS="$([ -f $topsrcdir/build/client.py-args ] && cat $topsrcdir/build/client.py-args)"
 mk_add_options ALWAYS_RUN_CLIENT_PY=1
 
 # XXX hack to work around dsymutil failing on OSX builds (bug 1380381, 1382262)
 ac_add_options RUSTFLAGS='-C debuginfo=1'
-
-# Disable stylo.
-# https://bugzilla.mozilla.org/show_bug.cgi?id=1380171
-ac_add_options --disable-stylo
-
-unset LLVM_CONFIG

--- a/mail/config/mozconfigs/macosx64/l10n-mozconfig
+++ b/mail/config/mozconfigs/macosx64/l10n-mozconfig
@@ -15,14 +15,8 @@ MOZ_ADDON_SIGNING=0
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Run client.py
 mk_add_options CLIENT_PY_ARGS="$([ -f $topsrcdir/build/client.py-l10n-args ] && cat $topsrcdir/build/client.py-l10n-args)"
 mk_add_options ALWAYS_RUN_CLIENT_PY=1
 
 # XXX hack to work around dsymutil failing on OSX builds (bug 1380381, 1382262)
 ac_add_options RUSTFLAGS='-C debuginfo=1'
-
-# Disable stylo.
-# https://bugzilla.mozilla.org/show_bug.cgi?id=1380171
-ac_add_options --disable-stylo
-
-unset LLVM_CONFIG

--- a/mail/config/mozconfigs/macosx64/nightly
+++ b/mail/config/mozconfigs/macosx64/nightly
@@ -34,14 +34,8 @@ MOZ_REQUIRE_ADDON_SIGNING=0
 ac_add_options --with-ccache
 
 # Run client.py
 mk_add_options CLIENT_PY_ARGS="$([ -f $topsrcdir/build/client.py-args ] && cat $topsrcdir/build/client.py-args)"
 mk_add_options ALWAYS_RUN_CLIENT_PY=1
 
 # XXX hack to work around dsymutil failing on OSX builds (bug 1380381, 1382262)
 ac_add_options RUSTFLAGS='-C debuginfo=1'
-
-# Disable stylo.
-# https://bugzilla.mozilla.org/show_bug.cgi?id=1380171
-ac_add_options --disable-stylo
-
-unset LLVM_CONFIG

--- a/mail/config/mozconfigs/macosx64/release
+++ b/mail/config/mozconfigs/macosx64/release
@@ -31,14 +31,8 @@ MOZ_REQUIRE_ADDON_SIGNING=0
 export MOZ_PACKAGE_JSSHELL=1
 
 # Run client.py
 mk_add_options CLIENT_PY_ARGS="$([ -f $topsrcdir/build/client.py-args ] && cat $topsrcdir/build/client.py-args)"
 mk_add_options ALWAYS_RUN_CLIENT_PY=1
 
 # XXX hack to work around dsymutil failing on OSX builds (bug 1380381, 1382262)
 ac_add_options RUSTFLAGS='-C debuginfo=1'
-
-# Disable stylo.
-# https://bugzilla.mozilla.org/show_bug.cgi?id=1380171
-ac_add_options --disable-stylo
-
-unset LLVM_CONFIG

--- a/mail/config/mozconfigs/win32/debug
+++ b/mail/config/mozconfigs/win32/debug
@@ -1,10 +1,11 @@
 . "$topsrcdir/build/mozconfig.win-common"
 . "$topsrcdir/build/mozconfig.common"
+. "$topsrcdir/build/mozconfig.stylo"
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-debug
 ac_add_options --enable-calendar
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 

--- a/mail/config/mozconfigs/win32/l10n-mozconfig
+++ b/mail/config/mozconfigs/win32/l10n-mozconfig
@@ -1,9 +1,10 @@
 . "$topsrcdir/build/mozconfig.common"
+. "$topsrcdir/build/mozconfig.stylo"
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --with-l10n-base=../../l10n
 # The compile environment is needed for Windows, see bug 1345422 comment #58.
 # ac_add_options --disable-compile-environment
 
 # Build lightning locales

--- a/mail/config/mozconfigs/win32/nightly
+++ b/mail/config/mozconfigs/win32/nightly
@@ -1,10 +1,11 @@
 . "$topsrcdir/build/mozconfig.win-common"
 . "$topsrcdir/build/mozconfig.common"
+. "$topsrcdir/build/mozconfig.stylo"
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --enable-jemalloc
 ac_add_options --enable-profiling
 ac_add_options --enable-calendar
 
 # For NSS symbols

--- a/mail/config/mozconfigs/win32/release
+++ b/mail/config/mozconfigs/win32/release
@@ -1,10 +1,11 @@
 . "$topsrcdir/build/mozconfig.win-common"
 . "$topsrcdir/build/mozconfig.common"
+. "$topsrcdir/build/mozconfig.stylo"
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --enable-jemalloc
 ac_add_options --enable-official-branding
 ac_add_options --enable-calendar
 
 # For NSS symbols

--- a/mail/config/mozconfigs/win64/debug
+++ b/mail/config/mozconfigs/win64/debug
@@ -1,10 +1,11 @@
 . "$topsrcdir/build/mozconfig.win-common"
 . "$topsrcdir/build/mozconfig.common"
+. "$topsrcdir/build/mozconfig.stylo"
 
 ac_add_options --target=x86_64-pc-mingw32
 ac_add_options --host=x86_64-pc-mingw32
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-debug
 ac_add_options --enable-calendar
 

--- a/mail/config/mozconfigs/win64/l10n-mozconfig
+++ b/mail/config/mozconfigs/win64/l10n-mozconfig
@@ -1,9 +1,10 @@
 . "$topsrcdir/build/mozconfig.common"
+. "$topsrcdir/build/mozconfig.stylo"
 
 ac_add_options --target=x86_64-pc-mingw32
 ac_add_options --host=x86_64-pc-mingw32
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 # The compile environment is needed for Windows, see bug 1345422 comment #58.
 # ac_add_options --disable-compile-environment

--- a/mail/config/mozconfigs/win64/nightly
+++ b/mail/config/mozconfigs/win64/nightly
@@ -1,10 +1,11 @@
 . "$topsrcdir/build/mozconfig.win-common"
 . "$topsrcdir/build/mozconfig.common"
+. "$topsrcdir/build/mozconfig.stylo"
 
 ac_add_options --target=x86_64-pc-mingw32
 ac_add_options --host=x86_64-pc-mingw32
 
 ac_add_options --enable-application=mail
 ac_add_options --enable-update-channel=${MOZ_UPDATE_CHANNEL}
 ac_add_options --enable-jemalloc
 ac_add_options --enable-profiling