PR middle-end/48591
	* omp-low.c (expand_omp_atomic_fetch_op): Return false if decl is
	NULL.
	(expand_omp_atomic_pipeline): Return false if cmpxchg is NULL.

	* gcc.dg/gomp/pr48591.c: New test.

	* testsuite/libgomp.c/pr48591.c: New test.

From-SVN: r172379