Bug 1284803 part 7 - Disable assembly if toolchain doesn't support ssse3/sse4.1 r=jesup

media/libyuv/libyuv.gyp

@@ -25,6 +25,7 @@
     'clang%': 0,
     # Link-Time Optimizations.
     'use_lto%': 0,
+    'yuv_disable_asm%': 0,
     'build_neon': 0,
     'conditions': [
        ['(target_arch == "armv7" or target_arch == "armv7s" or \
@@ -80,6 +81,14 @@
             }],
           ],
         }],
+        [ 'yuv_disable_asm != 0', {
+          'defines': [
+            # Enable the following 3 macros to turn off assembly for specified CPU.
+            'LIBYUV_DISABLE_X86',
+            'LIBYUV_DISABLE_NEON',
+            'LIBYUV_DISABLE_MIPS',
+          ],
+        }],
         ['build_with_mozilla == 1', {
           'defines': [
             'HAVE_JPEG'