re PR middle-end/29947 (OpenMP parallel for fails for reversed loop range)

	PR libgomp/29947
	* omp-low.c (expand_omp_for_static_nochunk,
	expand_omp_for_static_chunk): Do all arithmetics in signed rather than
	unsigned type.

	* loop.c (gomp_loop_init): Make parameters signed.  Set ws->end to
	start if there shouldn't be any loop iterations.
	(gomp_loop_ordered_static_start): Remove start == end test.
	* testsuite/libgomp.c/pr29947-1.c: New test.
	* testsuite/libgomp.c/pr29947-2.c: New test.

From-SVN: r119485