intel/compiler: Clean ups and micro optimizations

This is a series of clean ups and micro optimizations to the Intel compiler backend. These help performance on a subset of Vulkan CTS and on the shaders from Batman Arkham City GOTY. I picked that particular set of shaders because it is the largest / longest running fossil in my fossil-db.

There will be another MR later today or tomorrow that will explain why I wanted to try to improve perf here.