These test cases being 'dg-skip-if [...] { ! amdgcn-*-* }' meant they were
only ever considered for 'amdgcn-*-*' target -- that is, GCN *target*, not
GCN *offload target*, what is intended to be tested here, but for which they
thus always were UNSUPPORTED. Use the same style of 'dg-[...]' directives
as for the nvptx offloading test cases, 'libgomp.c/declare-variant-3*.c'.
Fix-up for commit 1fd508744e
"amdgcn: Support AMD-specific 'isa' traits in OpenMP context selectors".
libgomp/
* testsuite/libgomp.c/declare-variant-4-fiji.c: Adjust.
* testsuite/libgomp.c/declare-variant-4-gfx803.c: Likewise.
* testsuite/libgomp.c/declare-variant-4-gfx900.c: Likewise.
* testsuite/libgomp.c/declare-variant-4-gfx906.c: Likewise.
* testsuite/libgomp.c/declare-variant-4-gfx908.c: Likewise.
* testsuite/libgomp.c/declare-variant-4-gfx90a.c: Likewise.
* testsuite/libgomp.c/declare-variant-4.h: Likewise.
* testsuite/libgomp.c/declare-variant-4.c: New.
aae57a9e19