c++: Tweak tsubst_qualified_id location.

c++: Tweak tsubst_qualified_id location.

Retain the location when tsubstituting a qualified-id so that our
static_assert diagnostic can benefit.  Don't create useless location
wrappers for temporary variables.

gcc/ChangeLog:

	PR c++/97518
	* tree.c (maybe_wrap_with_location): Don't add a location
	wrapper around an artificial and ignored decl.

gcc/cp/ChangeLog:

	PR c++/97518
	* pt.c (tsubst_qualified_id): Use EXPR_LOCATION of the qualified-id.
	Use it to maybe_wrap_with_location the final expression.

gcc/testsuite/ChangeLog:

	PR c++/97518
	* g++.dg/diagnostic/static_assert3.C: New test.