Fix PR middle-end/98082

Fix PR middle-end/98082

this fixes an ICE introduced by the fix for PR middle-end/97078 where
use_register_for_decl was changed to return true at -O0 for a parameter
of a thunk.  It turns out that we need to do the same for a result in
this case.

gcc/ChangeLog:
	PR middle-end/98082
	* function.c (use_register_for_decl): Also return true for a result
	if cfun->tail_call_marked is true.

gcc/testsuite/ChangeLog:
	* g++.dg/cpp2a/pr98082.C: New test.