--- a/build/macosx/cross-mozconfig.common
+++ b/build/macosx/cross-mozconfig.common
@@ -24,16 +24,17 @@ CROSS_SYSROOT=$topsrcdir/MacOSX10.7.sdk
 CROSS_PRIVATE_FRAMEWORKS=$CROSS_SYSROOT/System/Library/PrivateFrameworks
 FLAGS="-target x86_64-apple-darwin11 -B $CROSS_CCTOOLS_PATH/bin -isysroot $CROSS_SYSROOT"
 
 export CC="$topsrcdir/clang/bin/clang $FLAGS"
 export CXX="$topsrcdir/clang/bin/clang++ $FLAGS"
 export CPP="$topsrcdir/clang/bin/clang $FLAGS -E"
 export LLVMCONFIG=$topsrcdir/clang/bin/llvm-config
 export LDFLAGS="-Wl,-syslibroot,$CROSS_SYSROOT -Wl,-dead_strip"
+export BINDGEN_CFLAGS="$FLAGS"
 export TOOLCHAIN_PREFIX=$CROSS_CCTOOLS_PATH/bin/x86_64-apple-darwin11-
 export DSYMUTIL=$topsrcdir/clang/bin/llvm-dsymutil
 export MKFSHFS=$topsrcdir/hfsplus-tools/newfs_hfs
 export DMG_TOOL=$topsrcdir/dmg/dmg
 export HFS_TOOL=$topsrcdir/dmg/hfsplus
 
 export HOST_CC="$topsrcdir/clang/bin/clang"
 export HOST_CXX="$topsrcdir/clang/bin/clang++"

--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -892,16 +892,30 @@ include('compile-checks.configure')
 @depends(have_64_bit,
          try_compile(body='static_assert(sizeof(void *) == 8, "")',
                      check_msg='for 64-bit OS'))
 def check_have_64_bit(have_64_bit, compiler_have_64_bit):
     if have_64_bit != compiler_have_64_bit:
         configure_error('The target compiler does not agree with configure '
                         'about the target bitness.')
 
+option(env='BINDGEN_CFLAGS',
+       nargs=1,
+       help='Options bindgen should pass to the C/C++ parser')
+
+@depends('BINDGEN_CFLAGS')
+@checking('bindgen cflags', lambda s: s if s and s.strip() else 'no')
+def bindgen_cflags(value):
+    if value and len(value):
+        # Reformat the env value for substitution into a toml list.
+        flags = value[0].split()
+        return ', '.join('"' + flag + '"' for flag in flags)
+    return ''
+
+set_config('BINDGEN_CFLAGS', bindgen_cflags)
 
 @depends(c_compiler)
 def default_debug_flags(compiler_info):
     # Debug info is ON by default.
     if compiler_info.type in ('msvc', 'clang-cl'):
         return '-Zi'
     return '-g'
 

new file mode 100644
--- /dev/null
+++ b/layout/style/bindgen.toml.in
@@ -0,0 +1,4 @@
+[build]
+args = [
+    @BINDGEN_CFLAGS@
+]

--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@@ -310,8 +310,12 @@ if CONFIG['COMPILE_ENVIRONMENT']:
         'nsCSSPropsGenerated.inc',
     ]
     css_props = GENERATED_FILES['nsCSSPropsGenerated.inc']
     css_props.script = 'GenerateCSSPropsGenerated.py:generate'
     css_props.inputs = [
         'nsCSSPropsGenerated.inc.in',
         'PythonCSSProps.h',
     ]
+
+    CONFIGURE_SUBST_FILES += [
+        'bindgen.toml',
+    ]