llvmpipe: do IR counting for shader cache management after optimization.

llvmpipe: do IR counting for shader cache management after optimization.

2ea923cf571235dfe573c35c3f0d90f632bd86d8 had the side effect of IR counting
now being done after IR optimization instead of before. Some quick analysis
shows that there's roughly 1.5 times more IR instructions before optimization
than after, hence the effective shader cache size got quite a bit smaller.
Could counter this with an increase of the instruction limit but it probably
makes more sense to count them after optimizations, so move that code.

Reviewed-by: Brian Paul <brianp@vmware.com>