Strengthen a few OpenACC test cases

Strengthen a few OpenACC test cases

Rather than rubber-stamp whatever requested vs. actual device kernel launch
configuration happens, actually (again) verify the requested values (modulo
expected variations).

This better highlights that "AMD GCN has an upper limit of 'num_workers(16)'",
and the deficiency that "AMD GCN uses the autovectorizer for the vector
dimension: the use of a function call in vector-partitioned code [...] is not
currently supported".

And, this removes several instances of race conditions, where variables are
concurrently written to in OpenACC gang-redundant mode.

	libgomp/
	* testsuite/libgomp.oacc-c-c++-common/loop-gwv-1.c: Strengthen.
	* testsuite/libgomp.oacc-c-c++-common/loop-gwv-2.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-red-gwv-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-red-v-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-red-v-2.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-red-w-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-red-w-2.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-red-wv-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-v-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-w-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-wv-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/routine-gwv-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/routine-v-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/routine-w-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/routine-wv-1.c: Likewise.