Only request C++11 when compiling C++ code.

build/standalone.gypi

 # Copyright 2014 PDFium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Definitions to be used when building stand-alone PDFium binaries.
 
 {
   'variables': {
     'component%': 'static_library',
     'clang%': 0,
@@ skipping 132 matching lines @@
     'defines!': [
       'DEBUG',
     ],
     'cflags': [
       '-Wall',
       '-W',
       '-Wno-unused-parameter',
       '-pthread',
       '-fno-exceptions',
       '-fvisibility=hidden',
-      '-std=gnu++0x',
     ],
     'cflags_cc': [
+      '-std=gnu++0x',
       '-Wnon-virtual-dtor',
       '-fno-rtti',
     ],
     'ldflags': [
       '-pthread',
     ],
     'msvs_cygwin_dirs': ['<(DEPTH)/v8/third_party/cygwin'],
     'msvs_configuration_attributes': {
       'OutputDirectory': '<(DEPTH)\\build\\$(ConfigurationName)',
       'IntermediateDirectory': '$(OutDir)\\obj\\$(ProjectName)',
@@ skipping 97 matching lines @@
           }],
         ],  # target_conditions
       },  # target_defaults
     }],  # OS=="mac"
   ],
   'xcode_settings': {
     # See comment in Chromium's common.gypi for why this is needed.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   }
 }