Also test -O0 for OpenACC C, C++ offloading test cases

Also test -O0 for OpenACC C, C++ offloading test cases

	libgomp/
	* testsuite/libgomp.oacc-c++/c++.exp: Set up torture testing, use
	gcc-dg-runtest.
	* testsuite/libgomp.oacc-c/c.exp: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/acc-on-device-2.c: Specify
	-fno-builtin-acc_on_device instead of -O0.
	* testsuite/libgomp.oacc-c-c++-common/acc-on-device.c: Skip for
	-O0.
	* testsuite/libgomp.oacc-c-c++-common/loop-auto-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-dim-default.c:
	Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-g-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-g-2.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-gwv-1.c: Likewise.
	* testsuite/libgomp.oacc-c-c++-common/loop-red-g-1.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-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-g-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.
	* testsuite/libgomp.oacc-c-c++-common/kernels-alias-ipa-pta-2.c:
	Don't specify -O2.
	* testsuite/libgomp.oacc-c-c++-common/kernels-alias-ipa-pta-3.c:
	Likewise.
	* testsuite/libgomp.oacc-c-c++-common/kernels-alias-ipa-pta.c:
	Likewise.

From-SVN: r234471