[PATCH 1/1] Rework atomic ops to use clang builtins rather than llvm asm

No changes in piglit pass rates for either turks or carrizo/iceland.

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>

Looks good to me.

no change in CTS 1.2 pass rate before/after this patch on pitcairn.

--Aaron