mesa: Actually use the Mesa IR optimizer for ARB programs.

mesa: Actually use the Mesa IR optimizer for ARB programs.

On Haswell, this cuts 1-3 instructions from 183 vertex shaders in
"Shadowrun Returns", "Shatter", and "Trine 2."  It adds 2 instructions
to a single fragment shader in "Closure."

total instructions in shared programs: 278803 -> 278546 (-0.09%)
instructions in affected programs:     41930 -> 41673 (-0.61%)

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>