Revert of GYP groudwork for half-float opts support.

Revert of GYP groudwork for half-float opts support. (patchset #1 id:1 of https://codereview.chromium.org/915693002/)

Reason for revert:
Going to punt on 16-bit float support for now.  Can't figure out ARM 64.

Original issue's description:
> GYP groudwork for half-float opts support.
> 
> This sets us up two new opts targets with the immediate goal of adding half-float (SkHalf.h) opts:
>   - opts_neon_fp16: uses hardware support on most ARM chips with NEON to do 4 conversions at a time;
>   - opts_avx: uses hardware support on Intel chips with AVX to do 8 conversions at a time.
> 
> opts_avx will be a handy thing to have around later too, especially if we want to work with floats.
> 
> This doesn't actually add any new source files to these libraries yet, so they're no-ops for now.
> I'll need to write a parallel change to Chrome's GN and GYPs before we can start adding sources.
> 
> This also rolls GYP up to head, to get suppport for EnableEnhancedInstructionSet: '3' on Windows,
> which is how we turn on AVX there.  There's no Mac-specific flag, so we use OTHER_CPLUSPLUSFLAGS.
> 
> BUG=skia:
> 
> TBR=reed@google.com
> 
> Committed: https://skia.googlesource.com/skia/+/46b80833394d7919cadf2abf2b93802141dd21c5

TBR=reed@google.com,mtklein@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Committed: https://skia.googlesource.com/skia/+/d160192fd9bab3c81d2dc40dbed41cdd7d660988

[mtklein, 2015-02-11 02:17:34]

Created Revert of GYP groudwork for half-float opts support.

[commit-bot: I haz the power, 2015-02-11 02:18:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/912223002/1

[commit-bot: I haz the power, 2015-02-11 02:18:21]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/d160192fd9bab3c81d2dc40dbed41cdd7d660988