Correct cmake intrinsic flag translation.

MSVC only. Use the AVX/AVX2 flags only for AVX and AVX2. Ignore
the SSE flags since they're not needed with MSVC.

BUG=https://bugs.chromium.org/p/aomedia/issues/detail?id=76

Change-Id: I0f3ac40ffb1f9c53a16272f0781df176317732f6
1 file changed