c++: Fix [[deprecated]] and implicit operator==. [PR97358]

c++: Fix [[deprecated]] and implicit operator==. [PR97358]

Trying to diagnose the problem with an implicit copy function breaks if the
function isn't actually a copy function.

gcc/cp/ChangeLog:

	PR c++/95844
	* decl.c (copy_fn_p): Return false for a function that is neither a
	constructor nor an assignment operator.
	(move_signature_fn_p): Likewise.

gcc/testsuite/ChangeLog:

	PR c++/95844
	* g++.dg/cpp2a/spaceship-eq10.C: New test.