avx and avx2 detection

This doesn't do anything yet beyond print out a message in Debug mode,
but it's a start.  Those messages should match the -SSE4-, -AVX-, or -AVX2- in
the Test-...-Debug-Trybots below.  The Release ones are just running by accident.

So far they look right to me.

BUG=skia:

Review URL: https://codereview.chromium.org/1428153003
1 file changed