RFA (Makefiles): PATCH to include libcpp and libiberty in GCC etags

[Jason Merrill]

Periodically I try to use M-. to pull up a function from libcpp and am 
frustrated that it doesn't work.  This patch fixes that, and throws in 
libiberty for good measure.

I also considered using --include for the TAGS files in those 
directories, but that would require people to 'make TAGS' separately in 
those directories for it to work, so I decided to go this way instead.

OK for trunk?
commit 9f68b2e2d4ccd5f9522ac33e42882fa2e60332a3
Author: Jason Merrill <ja...@redhat.com>
Date:   Wed Oct 28 13:29:32 2015 -0400

    comment

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 2745b40..a37e516 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -23476,6 +23476,7 @@ do_auto_deduction (tree type, tree init, tree auto_node,
     }
   else
     {
+      // multiple autos: walk all autos and replace/collect them into parms
       tree parms = build_tree_list (NULL_TREE, type);
       tree tparms = make_tree_vec (1);
       int val;