Bug 1194905 - Build libvpx neon code without -mthumb and -mfloat-abi=softfp. r=mshal

-mfloat-abi=softfp is hardcoding an ABI that may not match everything else
in Gecko, which is bound to fail. It's also unrelated to building NEON code.
-mthumb is also unrelated to building NEON code, and should be left as it
is for everything else.
Now, interestingly, we also have a VPX_ASFLAGS variable that just contains
the right things instead of hardcoding them in the moz.build, so just use
that instead.

media/libvpx/moz.build

@@ -45,7 +45,7 @@ if CONFIG['VPX_ARM_ASM']:
 
     for f in SOURCES:
         if f.endswith('.c') and 'neon' in f:
-            SOURCES[f].flags += ['-march=armv7-a', '-mthumb', '-mfloat-abi=softfp', '-mfpu=neon']
+            SOURCES[f].flags += CONFIG['VPX_ASFLAGS']
 
 # boolhuff_armv5te.asm defines the same functions as boolhuff.c instead of
 # using RTCD, so we have to make sure we only add one of the two.