GCN, nvptx: Define '_Unwind_DeleteException'

GCN, nvptx: Define '_Unwind_DeleteException'

This resolves GCN:

    ld: error: undefined symbol: _Unwind_DeleteException
    >>> referenced by eh_catch.cc:109 ([...]/source-gcc/libstdc++-v3/libsupc++/eh_catch.cc:109)
    >>>               eh_catch.o:(__cxa_end_catch) in archive [...]/build-gcc/amdgcn-amdhsa/libstdc++-v3/src/.libs/libstdc++.a
    [...]
    collect2: error: ld returned 1 exit status

..., and nvptx:

    unresolved symbol _Unwind_DeleteException
    collect2: error: ld returned 1 exit status

For both GCN, nvptx, this each progresses ~100 'check-gcc-c++',
and ~500 'check-target-libstdc++-v3' test cases:

    [-FAIL:-]{+PASS:+} [...] (test for excess errors)

..., with (if applicable, for most of them):

    [-UNRESOLVED:-]{+PASS:+} [...] [-compilation failed to produce executable-]{+execution test+}

..., or just a few 'FAIL: [...] execution test' where these test cases now
FAIL for unrelated reasons, or, if applicable, FAIL due to run-time
'GCC/nvptx: sorry, unimplemented: dynamic stack allocation not supported'.

	libgcc/
	* config/gcn/unwind-gcn.c (_Unwind_DeleteException): New.
	* config/nvptx/unwind-nvptx.c (_Unwind_DeleteException): Likewise.

(cherry picked from commit 815abd68353751d53ed9299e218f8ca1cc108d5f)