Tweak -mssse3 on Mac a little.

Using OTHER_CPLUSPLUSFLAGS instead of OTHER_CFLAGS will append -mssse3 into the
argument list instead of overwriting as the old note warns about.  (So it's
actually there twice now for the files in opts_ssse3, and we can still build if
we remove -mssse3 from common_conditions.gypi.)

We could also just delete this clause entirely given that
common_conditions.gypi sets it anyway.  Which do you think is best?  This code
won't compile unless _someone_ has set -mssse3.  Seems to me the redundancy
helps communicate that and protect against changes in common_conditions.gypi.

BUG=
R=epoger@google.com, bungeman@google.com

Author: mtklein@google.com

Review URL: https://chromiumcodereview.appspot.com/21279005

git-svn-id: http://skia.googlecode.com/svn/trunk@10573 2bbb7eff-a529-9590-31e7-b0007b416f81

gyp/opts.gyp

@@ -122,14 +122,7 @@
             '-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)
-        [ 'skia_os in ["mac"]', {
-          'xcode_settings': {
-            'OTHER_CFLAGS': ['-mssse3',],
-          },
-        }],
+        # (Mac has -mssse3 globally.)
         [ 'skia_arch_type == "x86"', {
           'sources': [
             '../src/opts/SkBitmapProcState_opts_SSSE3.cpp',