Fix 'libgomp.c/simd-math-1.c' configuration, again

Fix 'libgomp.c/simd-math-1.c' configuration, again

Tobias pointed out that as of my recent
og12 commit e7d4bcb974915bfe95be6c385641fc66a4201581
"Fix 'libgomp.c/simd-math-1.c' configuration",
in GCC configurations without GCN offloading configured, we'd get:

    xgcc: error: GCC is not configured to support 'amdgcn-amdhsa' as '-foffload=' argument

("Interestingly", GCC doesn't complain for '-foffload-options=-lm' if there are
no offload targets configured...)

	libgomp/
	* testsuite/libgomp.c/simd-math-1.c: Fix configuration, again.