c++: Fix exported using decls of templates

We need to look at DECL_TEMPLATE_RESULT to get the module attachment.

	PR c++/106849

gcc/cp/ChangeLog:

	* name-lookup.cc (do_nonmember_using_decl): Handle
	TEMPLATE_DECLs when checking module attachment.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/using-9.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Signed-off-by: Nathan Sidwell <nathan@acm.org>