[nvptx, libgomp] Move rtl-dump test-cases to libgomp

[nvptx, libgomp] Move rtl-dump test-cases to libgomp

The goacc.exp test-cases nvptx-merged-loop.c and nvptx-sese-1.c are failing
during linking due to missing libgomp.spec.

Move them to the libgomp testsuite.

Build and reg-tested on x86_64 with nvptx accelerator.

2018-12-19  Tom de Vries  <tdevries@suse.de>

	* gcc.dg/goacc/nvptx-merged-loop.c: Move to
	libgomp/testsuite/libgomp.oacc-c-c++-common.
	* gcc.dg/goacc/nvptx-sese-1.c: Same.

	* testsuite/lib/libgomp.exp: Add load_lib of scanoffloadrtl.exp.
	* testsuite/libgomp.oacc-c-c++-common/nvptx-merged-loop.c: Move from
	gcc/testsuite/gcc.dg/goacc.
	* testsuite/libgomp.oacc-c-c++-common/nvptx-sese-1.c: Same.

From-SVN: r267267