PR c/68966 - atomic_fetch_* on atomic_bool not diagnosed

PR c/68966 - atomic_fetch_* on atomic_bool not diagnosed

gcc/ChangeLog:
	* doc/extend.texi (__atomic Builtins, __sync Builtins): Document
	constraint on the type of arguments.

gcc/c-family/ChangeLog:
	* c-common.c (sync_resolve_size): Reject first argument when it's
	a pointer to _Bool.

gcc/testsuite/ChangeLog:
	* gcc.dg/atomic-fetch-bool.c: New test.
	* gcc.dg/sync-fetch-bool.c: New test.

From-SVN: r232147