Fix compute_reloc_for_constant

[Jan Hubicka]

Hi,
while comparing LTO and non-LTO builds I noticed that with LTO we produce a lot
more vtables in datal.rel.ro rather than data.rel.ro.local
This is because of partitioning promoting more symbols global. For RTL we make
section decisions based on SYMBOL_REF_LOCAL_FLAG that is set based on
decl_binds_local_p.  For variables we use TREE_PUBLIC check that is overly
conservative.

Bootstrapped/regtested x86_64-linux, OK?
        * varasm.c (compute_reloc_for_constant): Use targetm.binds_local_p
        instead of TREE_PUBLIC to determine if reference will be local
        within given DSO or not.
Index: varasm.c
===================================================================
--- varasm.c    (revision 206684)
+++ varasm.c    (working copy)
@@ -4060,7 +4060,7 @@
          break;
        }
 
-      if (TREE_PUBLIC (tem))
+      if (!targetm.binds_local_p (tem))
        reloc |= 2;
       else
        reloc |= 1;