[PATCH 1/1] Implement cl_khr_int64_base_atomics builtins

Passes newly posted piglit tests on carrizo/iceland (after modding
clover to expose the extension)

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

Reviewed-by: Aaron Watry <awatry@gmail.com>
Tested-by: Aaron Watry <awatry@gmail.com>

I've tested this using the CL 1.2 CTS on PITCAIRN (GCN 1.0) after
exposing the extension in clover.

--Aaron