libclc: Add assembly versions of vstore for global [u]int4/8/16

The assembly should be generic, but at least currently R600 only supports
32-bit stores of [u]int1/4, and I believe that only global is well-supported.

R600 lowers the 8/16 component stores to multiple 4-component stores.

The unoptimized C versions of the other stuff is left in place.

Patch by: Aaron Watry

llvm-svn: 185009