c++: Fix resolving the address of overloaded pmf [PR96647]

c++: Fix resolving the address of overloaded pmf [PR96647]

In resolve_address_of_overloaded_function, currently only the second
pass over the overload set (which considers just the function templates
in the overload set) checks constraints and performs return type
deduction when necessary.  But as the testcases below show, we need to
do the same when considering non-template functions during the first
pass.

gcc/cp/ChangeLog:

	PR c++/96647
	* class.c (resolve_address_of_overloaded_function): Check
	constraints_satisfied_p and perform return-type deduction via
	maybe_instantiate_decl when considering non-template functions
	in the overload set.
	* cp-tree.h (maybe_instantiate_decl): Declare.
	* decl2.c (maybe_instantiate_decl): Remove static.

gcc/testsuite/ChangeLog:

	PR c++/96647
	* g++.dg/cpp0x/auto-96647.C: New test.
	* g++.dg/cpp0x/error9.C: New test.
	* g++.dg/cpp2a/concepts-fn6.C: New test.