Bug 1371016 - aom: Add /arch:AVX2 when compiling under msvc. r=ted

Propagate the libvpx AVX flag changes from bug 1279593.

This flag tells the compiler to generate AVX code
in these modules intead of using normal SSE instructions
which can trigger expensive state-switching.

NB: This should only be set for AVX-specific implementation
files; setting this flag for general code will invalidate
our runtime simd support checks.

MozReview-Commit-ID: 5BVeCTsNlup

--HG--
extra : rebase_source : 219b5912a220e960e45ec43a532f407fe18eb41b

media/libaom/moz.build

@@ -98,6 +98,13 @@ if CONFIG['CLANG_CL'] or not CONFIG['_MSC_VER']:
         elif f.endswith('avx2.c'):
             SOURCES[f].flags += ['-mavx2']
 
+if CONFIG['_MSC_VER'] and not config['CLANG_CL']:
+    for f in SOURCES:
+        if f.endswith('avx.c'):
+            SOURCES[f].flags += ['-arch:AVX']
+        if f.endswith('avx2.c'):
+            SOURCES[f].flags += ['-arch:AVX2']
+
 # Suppress warnings in third-party code.
 if CONFIG['GNU_CC'] or CONFIG['CLANG_CL']:
     CFLAGS += [