GitLab

The _avx.cpp code was working in a degraded (SSE2/SSSE3) mode silently.
This CL will make the _avx.cpp code start using AVX.

There is currently no _avx2.cpp code, but I'm writing some now,
and this change will make it work properly from the start.

Chrome and Android builds should already be okay.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1535443003
CQ_EXTRA_TRYBOTS=client.skia.compile:Build-Ubuntu-GCC-x86_64-Release-CMake-Trybot,Build-Mac10.9-Clang-x86_64-Release-CMake-Trybot

Review URL: https://codereview.chromium.org/1535443003