Add build targets for advanced Intel instruction sets (1.5 of 3)

Add build targets for advanced Intel instruction sets (1.5 of 3)

This is a follow-up to https://codereview.chromium.org/1290423007/,
with a couple small changes:

   - turn on AVX and AVX2 for Windows using /arch ('EnabledEnhancedInstructionSet')
   - reformat and de-conditionalize where possible / irrelevant

Picked up this while poking around in libvpx's Chrome GYPs.

And yes, AVX = 3, AVX2 = 5.  Don't even ask what 4 means...

BUG=skia:4117

Review URL: https://codereview.chromium.org/1309253002