2011-11-24  Andrew MacLeod  <amacleod@redhat.com>

	PR c/51256
	* c-common.c (get_atomic_generic_size): Check for various error 
	conditions
	(resolve_overloaded_atomic_exchange, 
	resolve_overloaded_atomic_compare_exchange, 
	resolve_overloaded_atomic_load, resolve_overloaded_atomic_store): Return
	error_mark_node for error conditions.
	* gcc.dg/atomic-pr51256.c: New.  Test error conditions.

From-SVN: r181709