c++: modules & using-decls

c++: modules & using-decls

This extends using-decls to modules.  In modules you can export a
using decl, but the exported decl must have external linkage already.
One thing you can do is export something from the GMF.

The novel thing is that now 'export using foo::bar;' *in namespace
bar* can mean something significant (rather than be an obscure nop).

	gcc/cp/
	* name-lookup.c (do_nonmember_using_decl): Add INSERT_P parm.
	Deal with exporting using decls.
	(finish_nonmember_using_decl): Examine BINDING_VECTOR.