re PR c++/52597 ([C++11] confusing diagnostics for invalid use of non-static member function in decltype)

	PR c++/52597
	* typeck.c (invalid_nonstatic_memfn_p): Use get_first_fn.  Take tree.
	* semantics.c (finish_decltype_type): Check it before type_unknown_p.
	* cp-tree.h: Adjust prototype.

From-SVN: r197131