[gcn] Set 'UI_NONE' for 'TARGET_EXCEPT_UNWIND_INFO' [PR94282]

In libgomp offloading testing, this resolves all the 'ld: error: undefined
symbol: __gxx_personality_v0' FAILs.

	gcc/
	PR target/94282
	* common/config/gcn/gcn-common.c (gcn_except_unwind_info): New
	function.
	(TARGET_EXCEPT_UNWIND_INFO): Define.
	libgomp/
	PR target/94282
	* testsuite/libgomp.c-c++-common/function-not-offloaded.c: Remove
	'dg-allow-blank-lines-in-output'.