Don't use WPO for the Clang builds.

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 5483 matching lines @@
             },
             'target_conditions': [
               ['optimize=="size"', {
                 'msvs_settings': {
                   'VCCLCompilerTool': {
                     # 1, optimizeMinSpace, Minimize Size (/O1)
                     'Optimization': '1',
                     # 2, favorSize - Favor small code (/Os)
                     'FavorSizeOrSpeed': '2',
                     'conditions': [
-                      ['full_wpo_on_official==1', {
+                      # TODO(thakis): Remove clang==0 here, crbug.com/598772
+                      ['full_wpo_on_official==1 and clang==0', {
                         # This implies link time code generation.
                         'WholeProgramOptimization': 'true',
                       }],
                     ],
                   },
                 },
               }],
               # This config is used to avoid a problem in ffmpeg, see
               # http://crbug.com/264459.
               ['optimize=="size_no_ltcg"', {
                 'msvs_settings': {
                   'VCCLCompilerTool': {
                     # 1, optimizeMinSpace, Minimize Size (/O1)
                     'Optimization': '1',
                     # 2, favorSize - Favor small code (/Os)
                     'FavorSizeOrSpeed': '2',
                   },
                 },
               }],
               ['optimize=="speed"', {
                 'msvs_settings': {
                   'VCCLCompilerTool': {
                     # 2, optimizeMaxSpeed, Maximize Speed (/O2)
                     'Optimization': '2',
                     # 1, favorSpeed - Favor fast code (/Ot)
                     'FavorSizeOrSpeed': '1',
                     'conditions': [
-                      ['full_wpo_on_official==1', {
+                      # TODO(thakis): Remove clang==0 here, crbug.com/598772
+                      ['full_wpo_on_official==1 and clang==0', {
                         # This implies link time code generation.
                         'WholeProgramOptimization': 'true',
                       }],
                     ],
                   },
                 },
               }],
               ['optimize=="max"', {
                 # Disable Warning 4702 ("Unreachable code") for the WPO/PGO
                 # builds. Probably anything that this would catch that
@@ skipping 783 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',
   },
 }