Add 'throw', caught test cases for GCN, nvptx target and OpenACC, OpenMP 'target...

Add 'throw', caught test cases for GCN, nvptx target and OpenACC, OpenMP 'target' offloading

	gcc/testsuite/
	* g++.target/gcn/exceptions-throw-2.C: New.
	* g++.target/nvptx/exceptions-throw-2.C: Likewise.
	libgomp/
	* testsuite/libgomp.c++/target-exceptions-throw-2.C: New.
	* testsuite/libgomp.c++/target-exceptions-throw-2-offload-sorry-GCN.C: Likewise.
	* testsuite/libgomp.c++/target-exceptions-throw-2-offload-sorry-nvptx.C: Likewise.
	* testsuite/libgomp.oacc-c++/exceptions-throw-2.C: Likewise.
	* testsuite/libgomp.oacc-c++/exceptions-throw-2-offload-sorry-GCN.C: Likewise.
	* testsuite/libgomp.oacc-c++/exceptions-throw-2-offload-sorry-nvptx.C: Likewise.

(cherry picked from commit 1daf57049878a79b8bb40fb57ee2370f3cd4d4e7)