Tweak -mssse3 on Mac a little.

gyp/opts.gyp

 {
   'targets': [
     # Due to an unfortunate intersection of lameness between gcc and gyp,
     # we have to build the *_SSE2.cpp files in a separate target.  The
     # gcc lameness is that, in order to compile SSE2 intrinsics code, it
     # must be passed the -msse2 flag.  However, with this flag, it may
     # emit SSE2 instructions even for scalar code, such as the CPUID
     # test used to test for the presence of SSE2.  So that, and all other
     # code must be compiled *without* -msse2.  The gyp lameness is that it
     # does not allow file-specific CFLAGS, so we must create this extra
@@ skipping 106 matching lines @@
       ],
       'include_dirs': [
         '../src/core',
       ],
       'conditions': [
         [ 'skia_os in ["linux", "freebsd", "openbsd", "solaris", "nacl", "chromeos"]', {
           'cflags': [
             '-mssse3',
           ],
         }],
-        # TODO(epoger): the following will enable SSSE3 on Macs, but it will
-        # break once we set OTHER_CFLAGS anywhere else (the first setting will
-        # be replaced, not added to)
+        # This is a little redundant, as common_conditions enables SSSE3 globally on Macs.
         [ 'skia_os in ["mac"]', {
           'xcode_settings': {
-            'OTHER_CFLAGS': ['-mssse3',],
+            'OTHER_CPLUSPLUSFLAGS': ['-mssse3',],

[epoger, 2013/08/06 15:38:32]

I don't understand how this is not susceptible to the same problem as
OTHER_CFLAGS.  If OTHER_CPLUSPLUSFLAGS has been set elsewhere, this will nuke
whatever settings were made to it...

Adding Ben Wagner as a reviewer, because I think he has a better understanding
of the issues than I do.  Ben, any clever ideas here?

           },
         }],
         [ 'skia_arch_type == "x86"', {
           'sources': [
             '../src/opts/SkBitmapProcState_opts_SSSE3.cpp',
           ],
         }],
       ],
     },
     # NEON code must be compiled with -mfpu=neon which also affects scalar
@@ skipping 37 matching lines @@
       ],
     },
   ],
 }
 
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