c++: xobj fn call without obj [PR115783]

c++: xobj fn call without obj [PR115783]

The code path for rejecting an object-less call to a non-static member
function should also consider xobj member functions (so that we correctly
reject the below calls with a "cannot call member function without object"
diagnostic).

	PR c++/115783

gcc/cp/ChangeLog:

	* call.cc (build_new_method_call): Generalize METHOD_TYPE
	check to DECL_OBJECT_MEMBER_FUNCTION_P.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp23/explicit-obj-diagnostics11.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>