c++: scoped variable template-id of reference type [PR97340]

c++: scoped variable template-id of reference type [PR97340]

lookup_and_finish_template_variable calls convert_from_reference, which
means for a variable template-id of reference type the function wraps
the corresponding VAR_DECL in an INDIRECT_REF.  But the downstream logic
of two callers, tsubst_qualified_id and finish_class_member_access_expr,
expect a DECL_P result and this unexpected INDIRECT_REF leads to an ICE
resolving such a (dependently scoped) template-id as in the first testcase.
(Note these two callers eventually call convert_from_reference on the
result anyway, so calling it earlier seems redundant in this case.)

This patch fixes this by pulling out the convert_from_reference call
from lookup_and_finish_template_variable and into the callers that
actually need it, which turns out to only be tsubst_copy_and_build
(if we got rid of the call there we'd mishandle the second testcase).

	PR c++/97340

gcc/cp/ChangeLog:

	* pt.cc (lookup_and_finish_template_variable): Don't call
	convert_from_reference.
	(tsubst_copy_and_build) <case TEMPLATE_ID_EXPR>: Call
	convert_from_reference on the result of
	lookup_and_finish_template_variable.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/var-templ80.C: New test.
	* g++.dg/cpp1y/var-templ81.C: New test.