Support alpha and color test masks on desktop/gles3

May help #3468 or possibly other issues.  Has a small performance impact but should only be for non-zero alphatests.

Some games possibly using it for alpha tests:
http://report.ppsspp.org/logs/kind/96

If I read correctly, GLSL 1.30 on desktop is where you can first use bitwise ops.

-[Unknown]