Re OpenACC "gang reduction on an orphan loop" error message

Re OpenACC "gang reduction on an orphan loop" error message

Follow-up to preceding commit 2b7dac2c0dcb087da9e4018943c023c0678234a3
"Make OpenACC orphan gang reductions errors".

	gcc/fortran/
	* openmp.c (oacc_is_parallel_or_serial): Evolve into...
	(oacc_is_compute_construct): ... this function.
	(resolve_oacc_loop_blocks): Use "oacc_is_compute_construct"
	instead of "oacc_is_parallel_or_serial" for checking that a
	loop is not orphaned.
	gcc/testsuite/
	* gfortran.dg/goacc/orphan-reductions-3.f90: New test
	verifying that the "gang reduction on an orphan loop" error message
	is not emitted for non-orphaned loops.
	* c-c++-common/goacc/orphan-reductions-3.c: Likewise for C and C++.

Co-Authored-By: Thomas Schwinge <thomas@codesourcery.com>