c++: visibility of local extern [PR103291]

When setting up the hidden namespace-scope decl for a local extern, we also
need to set its visibility.

	PR c++/103291

gcc/cp/ChangeLog:

	* name-lookup.cc (push_local_extern_decl_alias): Call
	determine_visibility.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/visibility/visibility-local-extern1.C: New test.