c++: redeclared hidden friend take 2 [PR105852]

c++: redeclared hidden friend take 2 [PR105852]

My previous patch for 105761 avoided copying DECL_TEMPLATE_INFO from a
friend to a later definition, but in this testcase we have first a
non-friend declaration and then a definition, and we need to avoid copying
in that case as well.  But we do still want to set new_template_info to
avoid GC trouble.

With this change, the modules dump correctly identifies ::foo as a
non-template function in tpl-friend-2_a.C.

Along the way I noticed that the duplicate_decls handling of
DECL_UNIQUE_FRIEND_P was backwards for templates, where we don't clobber
DECL_LANG_SPECIFIC (olddecl) with DECL_LANG_SPECIFIC (newdecl) like we do
for non-templates.

	PR c++/105852
	PR c++/105761

gcc/cp/ChangeLog:

	* decl.cc (duplicate_decls): Avoid copying template info
	from non-templated friend even if newdecl isn't a definition.
	Correct handling of DECL_UNIQUE_FRIEND_P on templates.
	* pt.cc (non_templated_friend_p): New.
	* cp-tree.h (non_templated_friend_p): Declare it.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/tpl-friend-2_a.C: Adjust expected dump.
	* g++.dg/template/friend74.C: New test.