GCN, nvptx: Support '-mfake-exceptions', and use it for offloading compilation [PR118794]

GCN, nvptx: Support '-mfake-exceptions', and use it for offloading compilation [PR118794]

With '-mfake-exceptions' enabled, the user-visible behavior in presence of
exception handling constructs changes such that the compile-time
'sorry, unimplemented: exception handling not supported' is skipped, code
generation proceeds, and instead, exception handling constructs 'abort' at
run time.  (..., or don't, if they're in dead code.)

	PR target/118794
	gcc/
	* config/gcn/gcn.opt (-mfake-exceptions): Support.
	* config/nvptx/nvptx.opt (-mfake-exceptions): Likewise.
	* config/gcn/gcn.md (define_expand "exception_receiver"): Use it.
	* config/nvptx/nvptx.md (define_expand "exception_receiver"):
	Likewise.
	* config/gcn/mkoffload.cc (main): Set it.
	* config/nvptx/mkoffload.cc (main): Likewise.
	* config/nvptx/nvptx.cc (nvptx_assemble_integer)
	<in_section == exception_section>: Special handling for
	'SYMBOL_REF's.
	* except.cc (expand_dw2_landing_pad_for_region): Don't generate
	bogus code for (default)
	'#define EH_RETURN_DATA_REGNO(N) INVALID_REGNUM'.
	libgcc/
	* config/gcn/unwind-gcn.c (_Unwind_Resume): New.
	* config/nvptx/unwind-nvptx.c (_Unwind_Resume): Likewise.
	gcc/testsuite/
	* g++.target/gcn/exceptions-bad_cast-2.C: Set
	'-mno-fake-exceptions'.
	* g++.target/gcn/exceptions-pr118794-1.C: Likewise.
	* g++.target/gcn/exceptions-throw-2.C: Likewise.
	* g++.target/nvptx/exceptions-bad_cast-2.C: Likewise.
	* g++.target/nvptx/exceptions-pr118794-1.C: Likewise.
	* g++.target/nvptx/exceptions-throw-2.C: Likewise.
	* g++.target/gcn/exceptions-bad_cast-2_-mfake-exceptions.C: New.
	* g++.target/gcn/exceptions-pr118794-1_-mfake-exceptions.C:
	Likewise.
	* g++.target/gcn/exceptions-throw-2_-mfake-exceptions.C: Likewise.
	* g++.target/nvptx/exceptions-bad_cast-2_-mfake-exceptions.C:
	Likewise.
	* g++.target/nvptx/exceptions-pr118794-1_-mfake-exceptions.C:
	Likewise.
	* g++.target/nvptx/exceptions-throw-2_-mfake-exceptions.C:
	Likewise.
	libgomp/
	* testsuite/libgomp.c++/target-exceptions-bad_cast-2-offload-sorry-GCN.C:
	Set '-foffload-options=-mno-fake-exceptions'.
	* testsuite/libgomp.c++/target-exceptions-bad_cast-2-offload-sorry-nvptx.C:
	Likewise.
	* testsuite/libgomp.c++/target-exceptions-pr118794-1-offload-sorry-GCN.C:
	Likewise.
	* testsuite/libgomp.c++/target-exceptions-pr118794-1-offload-sorry-nvptx.C:
	Likewise.
	* 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-bad_cast-2-offload-sorry-GCN.C:
	Likewise.
	* testsuite/libgomp.oacc-c++/exceptions-bad_cast-2-offload-sorry-nvptx.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.
	* testsuite/libgomp.c++/target-exceptions-bad_cast-2.C: Adjust.
	* testsuite/libgomp.c++/target-exceptions-pr118794-1.C: Likewise.
	* testsuite/libgomp.c++/target-exceptions-throw-2.C: Likewise.
	* testsuite/libgomp.oacc-c++/exceptions-bad_cast-2.C: Likewise.
	* testsuite/libgomp.oacc-c++/exceptions-throw-2.C: Likewise.
	* testsuite/libgomp.c++/target-exceptions-throw-2-O0.C: New.