c++: tweak to (*(fn))() patch [PR104618]

Other callers of mark_single_function might also want to look through these
wrapapers.

	PR c++/104618

gcc/cp/ChangeLog:

	* decl2.cc (mark_single_function): Look through parens and location
	wrapper.
	* typeck.cc (cp_build_addr_expr_1): Not here.