Pass clang flags to the host compiler, too.

build/common.gypi

 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 1483 matching lines @@
               ['_toolset=="target"', {
                 'cflags': [
                   '--sysroot=<(sysroot)',
                 ],
                 'ldflags': [
                   '--sysroot=<(sysroot)',
                 ],
               }]]
           }],
           ['clang==1', {
-            'target_conditions': [
-              ['_toolset=="target"', {
-                'cflags': [
-                  '-Wheader-hygiene',
-                  # Clang spots more unused functions.
-                  '-Wno-unused-function',
-                  # Don't die on dtoa code that uses a char as an array index.
-                  '-Wno-char-subscripts',
-                  # Survive EXPECT_EQ(unnamed_enum, unsigned int) -- see
-                  # http://code.google.com/p/googletest/source/detail?r=446 .
-                  # TODO(thakis): Use -isystem instead (http://crbug.com/58751 )
-                  '-Wno-unnamed-type-template-args',
-                ],
-                'cflags!': [
-                  # Clang doesn't seem to know know this flag.
-                  '-mfpmath=sse',
-                ],
-              }]],
+            'cflags': [
+              '-Wheader-hygiene',
+              # Clang spots more unused functions.
+              '-Wno-unused-function',
+              # Don't die on dtoa code that uses a char as an array index.
+              '-Wno-char-subscripts',
+              # Survive EXPECT_EQ(unnamed_enum, unsigned int) -- see
+              # http://code.google.com/p/googletest/source/detail?r=446 .
+              # TODO(thakis): Use -isystem instead (http://crbug.com/58751 )
+              '-Wno-unnamed-type-template-args',
+            ],
+            'cflags!': [
+              # Clang doesn't seem to know know this flag.
+              '-mfpmath=sse',
+            ],
           }],
           ['clang==1 and clang_use_chrome_plugins==1', {
             'target_conditions': [
               ['_toolset=="target"', {
                 'cflags': [
                   '<(clang_chrome_plugins_flags)',
                 ],
               }]],
           }],
           ['clang==1 and clang_load!="" and clang_add_plugin!=""', {
@@ skipping 402 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }