Fix Mac Breakpad host tools to build in Linux cross-compile

src/tools/mac/tools_mac.gypi

 # Copyright 2014 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 37 matching lines @@
       },
       'dependencies': [
         '../common/common.gyp:common',
         '../processor/processor.gyp:processor',
       ],
     },
     {
       'target_name': 'dump_syms',
       'type': 'executable',
       'sources': [
-        'dump_syms/dump_syms_tool.mm',
+        'dump_syms/dump_syms_tool.cc',
       ],
       'link_settings': {
         'libraries': [
           '$(SDKROOT)/System/Library/Frameworks/Foundation.framework',
         ],
       },
       'dependencies': [
         '../common/common.gyp:common',
       ],
     },
@@ skipping 38 matching lines @@
         'libraries': [
           '$(SDKROOT)/System/Library/Frameworks/Foundation.framework',
         ],
       },
       'dependencies': [
         '../common/common.gyp:common',
       ],
     },
   ],
 }