vc4: Flip the switch to run the GLSL compiler optimization loop once.

vc4: Flip the switch to run the GLSL compiler optimization loop once.

This has almost no effect on shader-db:

total instructions in shared programs: 92572 -> 92611 (0.04%)
instructions in affected programs:     4486 -> 4525 (0.87%)

Looking at 2 of the 7 different shaders that were hurt (all of which were
in mupen64), they all appear to be just differences in order of
instructions at the NIR level.

The advantage is that this should significantly reduce time in the compiler.