[gcn] Work-around libgomp 'error: array subscript 0 is outside array bounds of ‘__lds...

[gcn] Work-around libgomp 'error: array subscript 0 is outside array bounds of ‘__lds struct gomp_thread * __lds[0]’ [-Werror=array-bounds]' some more [PR101484]

With yesterday's commit 9f2bc5077debef2b046b6c10d38591ac324ad8b5 "[gcn]
Work-around libgomp 'error: array subscript 0 is outside array bounds of
‘__lds struct gomp_thread * __lds[0]’ [-Werror=array-bounds]' [PR101484]",
I did defuse the "unexpected" '-Werror=array-bounds' diagnostics that we see
as of commit a110855667782dac7b674d3e328b253b3b3c919b "Correct handling of
variable offset minus constant in -Warray-bounds [PR100137]".  However, these
'#pragma GCC diagnostic [...]' directives cause some code generation changes
(that seems unexpected, problematic!), which results in a lot (ten thousands)
of 'GCN team arena exhausted' run-time diagnostics, also leading to a few
FAILs:

    PASS: libgomp.c/../libgomp.c-c++-common/for-11.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-11.c execution test

    PASS: libgomp.c/../libgomp.c-c++-common/for-12.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-12.c execution test

    PASS: libgomp.c/../libgomp.c-c++-common/for-3.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-3.c execution test

    PASS: libgomp.c/../libgomp.c-c++-common/for-5.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-5.c execution test

    PASS: libgomp.c/../libgomp.c-c++-common/for-6.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-6.c execution test

    PASS: libgomp.c/../libgomp.c-c++-common/for-9.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-9.c execution test

Same for 'libgomp.c++'.

It remains to be analyzed how '#pragma GCC diagnostic [...]' directives can
cause code generation changes; for now I'm working around the "unexpected"
'-Werror=array-bounds' diagnostics differently.

Overall, still awaiting a different solution, of course.

	libgomp/
	PR target/101484
	* configure.tgt [amdgcn*-*-*] (XCFLAGS): Add
	'-Wno-error=array-bounds'.
	* config/gcn/team.c: Remove '-Werror=array-bounds' work-around.
	* libgomp.h [__AMDGCN__]: Likewise.