Update NEON compiler defines to use SK_ prefix

gyp/common_variables.gypi

 # Copyright 2012 The Android Open Source Project
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   # Get ready for the ugly...
   #
   # - We have to nest our variables dictionaries multiple levels deep, so that
   #   this and other gyp files can rely on previously-set variable values in
@@ skipping 75 matching lines @@
           'skia_arch_width%': 32,
         }],
         [ 'skia_os == "android"', {
           'skia_static_initializers%': 0,
         }, {
           'skia_static_initializers%': 1,
         }],
         [ 'skia_os == "ios"', {
           'skia_arch_type%': 'arm',
           'arm_version%': 7,
-          'arm_neon%': 0, # neon asm files known not to work with the ios build
+          'arm_neon_optional%': 1, 
         }],
         [ 'skia_os in ["android", "nacl"] and not skia_android_framework',
           # skia_freetype_static - on OS variants that normally would
           #     dynamically link the system FreeType library, don't do
           #     that; instead statically link to the version in
           #     third_party/freetype and third_party/externals/freetype.
           {
             'skia_freetype_static%': '1',
           }, {
             'skia_freetype_static%': '0',
@@ skipping 127 matching lines @@
     'skia_moz2d%': 0,
     'skia_crash_handler%':
         '<!(python -c "import os; print os.environ.get(\'CHROME_HEADLESS\', 0)")',
 
     # These are referenced by our .gypi files that list files (e.g. core.gypi)
     #
     'skia_src_path%': '../src',
     'skia_include_path%': '../include',
   },
 }