Jason realized that we could fix the result of the CMP instruction on
Gen <= 5 by doing -(result & 1). Also do the resolves in the vec4
backend before use, rather than when the bool was created. The FS does
this and it saves some unnecessary resolves.

On Ironlake:

total instructions in shared programs: 4289762 -> 4287277 (-0.06%)
instructions in affected programs:     619430 -> 616945 (-0.40%)

Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>