c++: attribute on dtor in template [PR108795]

Since r7-2549 we were throwing away the explicit C:: when we found that ~C
has an attribute that we treat as making its type dependent.

	PR c++/108795

gcc/cp/ChangeLog:

	* semantics.cc (finish_id_expression_1): Check scope before
	returning id_expression.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/attr-tsafe1.C: New test.