Handle target specific memory models in C frontend

Handle target specific memory models in C frontend

get_atomic_generic_size would error out for
__atomic_store(...,__ATOMIC_HLE_RELEASE)

Just mask it out. All the memory orders are checked completely
in builtins.c anyways.

I'm not sure what that check is for, it could be removed in theory.

Passed bootstrap and test suite on x86-64

gcc/c-family/:
2012-11-09  Andi Kleen  <ak@linux.intel.com>

	PR 55139
	* c-common.c (get_atomic_generic_size): Mask with
        MEMMODEL_MASK

From-SVN: r193363