[PR c++/59930] template friend injection
https://gcc.gnu.org/ml/gcc-patches/2017-12/msg01168.html
PR c++/59930
* name-lookup.c (name_lookup::search_unqualified): Don't search
parent namespace when looking for hidden things.
* pt.c (tsubst_friend_class): Always push to friend scope, drop
unneeded self-friend check. Inject new hidden friend into correct
scope.
PR c++/59930
* g++.dg/parse/pr81247-c.C: Adjust.
* g++.dg/template/pr59930-[123].C: New.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@255780 138bc75d-0d04-0410-961f-82ee72b054a4