Add test cases for exception handling constructs in dead code for GCN, nvptx target...

Add test cases for exception handling constructs in dead code for GCN, nvptx target and OpenMP 'target' offloading [PR118794]

	PR target/118794
	gcc/testsuite/
	* g++.target/gcn/exceptions-pr118794-1.C: New.
	* g++.target/nvptx/exceptions-pr118794-1.C: Likewise.
	libgomp/
	* testsuite/libgomp.c++/target-exceptions-pr118794-1.C: New.
	* testsuite/libgomp.c++/target-exceptions-pr118794-1-offload-sorry-GCN.C:
	Likewise.
	* testsuite/libgomp.c++/target-exceptions-pr118794-1-offload-sorry-nvptx.C:
	Likewise.

(cherry picked from commit aa3e72f943032e5f074b2bd2fd06d130dda8760b)