swr/rast: Add autogen of helper llvm intrinsics.

swr/rast: Add autogen of helper llvm intrinsics.

Replace sqrt, maskload, fp min/max, cttz, ctlz with llvm equivalent.
Replace AVX maskedstore intrinsic with LLVM intrinsic. Add helper llvm
macros for stacksave, stackrestore, popcnt.

Reviewed-by: Bruce Cherniak <bruce.cherniak@intel.com>