[libgomp] In OpenACC testing, cycle though all offload targets

[libgomp] In OpenACC testing, cycle though all offload targets

... instead of through offload plugins.

	libgomp/
	* plugin/configfrag.ac: Populate and AC_SUBST offload_targets.
	* testsuite/libgomp-test-support.exp.in: Adjust.
	* testsuite/lib/libgomp.exp: Likewise.  Don't populate
	openacc_device_types_s.
	(offload_target_to_openacc_device_type): New proc.
	* testsuite/libgomp.oacc-c++/c++.exp: Adjust.
	* testsuite/libgomp.oacc-c/c.exp: Likewise.
	* testsuite/libgomp.oacc-fortran/fortran.exp: Likewise.
	* Makefile.in: Regenerate.
	* configure: Likewise.
	* testsuite/Makefile.in: Likewise.

From-SVN: r269108