Don't remove -mfpmath=sse when building with clang.

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 3880 matching lines @@
               '-Wno-c++11-narrowing',
 
               # TODO(thakis): Remove, http://crbug.com/263960
               '-Wno-reserved-user-defined-literal',
 
               # Clang considers the `register` keyword as deprecated, but e.g.
               # code generated by flex (used in angle) contains that keyword.
               # http://crbug.com/255186
               '-Wno-deprecated-register',
             ],
-            'cflags!': [
-              # Clang doesn't seem to know know this flag.
-              '-mfpmath=sse',
-            ],
             'cflags_cc': [
               # See the comment in the Mac section for what it takes to move
               # this to -std=c++11.
               '-std=gnu++11',
             ],
           }],
           ['clang==1 and clang_use_chrome_plugins==1', {
             'cflags': [
               '<@(clang_chrome_plugins_flags)',
             ],
@@ skipping 1757 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',
   },
 }