c++: avoid duplicate deprecated warning [PR90451]

c++: avoid duplicate deprecated warning [PR90451]

We were getting the deprecated warning twice for the same call because we
called mark_used first in finish_qualified_id_expr and then again in
build_over_call.  Let's not call it the first time; C++17 clarified that a
function is used only when it is selected from an overload set, which
happens later.

Then I had to add a few more uses in places that don't do anything further
with the expression (convert_to_void, finish_decltype_type), and places that
use the expression more unusually (cp_build_addr_expr_1,
convert_nontype_argument).  The new mark_single_function is mostly so
that I only have to put the comment in one place.

	PR c++/90451

gcc/cp/ChangeLog:

	* decl2.cc (mark_single_function): New.
	* cp-tree.h: Declare it.
	* typeck.cc (cp_build_addr_expr_1): mark_used when making a PMF.
	* semantics.cc (finish_qualified_id_expr): Not here.
	(finish_id_expression_1): Or here.
	(finish_decltype_type): Call mark_single_function.
	* cvt.cc (convert_to_void): And here.
	* pt.cc (convert_nontype_argument): And here.
	* init.cc (build_offset_ref): Adjust assert.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/deprecated-14.C: New test.
	* g++.dg/warn/deprecated-15.C: New test.