clang/win: For 64-bit builds, enable warnings-as-errors and stop falling back to CL.

build/common.gypi

 # Copyright (c) 2012 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 5458 matching lines @@
             }],
             ['_type=="executable" and ">(win_exe_compatibility_manifest)"!=""', {
               'VCManifestTool': {
                 'AdditionalManifestFiles': [
                   '>(win_exe_compatibility_manifest)',
                 ],
               },
             }],
           ],
           'conditions': [
+            # Building with Clang on Windows is a work in progress and very
+            # experimental. See crbug.com/82385.
             ['clang==1', {
-              # Building with Clang on Windows is a work in progress and very
-              # experimental. See crbug.com/82385.
               'VCCLCompilerTool': {
-                'WarnAsError': 'false',
-                'RuntimeTypeInfo': 'false',
                 'AdditionalOptions': [
                   '-fmsc-version=1800',
-                  '/fallback',
 
                   # Many files use intrinsics without including this header.
                   # TODO(hans): Fix those files, or move this to sub-GYPs.
                   '/FIIntrin.h',
 
                   # TODO(hans): Make this list shorter eventually.
                   '-Qunused-arguments',
                   '-Wno-c++11-compat-deprecated-writable-strings',
                   '-Wno-deprecated-declarations',
                   '-Wno-empty-body',
@@ skipping 22 matching lines @@
                   '-Wno-unsequenced',
                   '-Wno-unused-function',
                   '-Wno-unused-private-field',
                   '-Wno-unused-value',
                   '-Wno-unused-variable',
                   '-Wno-unused-local-typedef',  # http://crbug.com/411648
                   '-Wno-inconsistent-missing-override', #http://crbug.com/428099
                 ],
               },
             }],
+            ['clang==1 and target_arch=="ia32"', {
+              'VCCLCompilerTool': {
+                'WarnAsError': 'false',
+                'AdditionalOptions': [
+                  '/fallback',
+                ],
+              },
+            }],
           ],
         },
       },
     }],
     ['disable_nacl==1', {
       'target_defaults': {
         'defines': [
           'DISABLE_NACL',
         ],
       },
@@ skipping 327 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',
   },
 }