intel/compiler: Micro optimize regions_overlap

intel/compiler: Micro optimize regions_overlap

On my Ice Lake laptop (using a locked CPU speed and other measures to
prevent thermal throttling, etc.) using a release build, improves
performance of compiling shaders from batman_arkham_city_goty.foz by
-1.09% ± 0.084% (n = 5, pooled s = 0.354471)

Reduces the size of a release build by 26k.

   text	   data	    bss	    dec	    hex	filename
23163641 400720	 231360	23795721	16b1809	before/lib64/dri/iris_dri.so
23137264 400720	 231360	23769344	16ab100	after/lib64/dri/iris_dri.so

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22299>