[GOOGLE] Emit linkage_name when built with -gmlt and for abstract decls

[Dehao Chen]

This patch emits linkage_name at -gmlt. It also make sure abstract
decls' linkage_names are emitted so that inlined functions can also
find linkage name.

Bootstrapped and passed regression test.

OK for google branches?

Thanks,
Dehao

Index: gcc/dwarf2out.c
===================================================================
--- gcc/dwarf2out.c (revision 201632)
+++ gcc/dwarf2out.c (working copy)
@@ -16537,10 +16537,9 @@ add_src_coords_attributes (dw_die_ref die, tree de
 static void
 add_linkage_name (dw_die_ref die, tree decl)
 {
-  if (debug_info_level > DINFO_LEVEL_TERSE
+  if (debug_info_level > DINFO_LEVEL_NONE
       && (TREE_CODE (decl) == FUNCTION_DECL || TREE_CODE (decl) == VAR_DECL)
       && TREE_PUBLIC (decl)
-      && !DECL_ABSTRACT (decl)
       && !(TREE_CODE (decl) == VAR_DECL && DECL_REGISTER (decl))
       && die->die_tag != DW_TAG_member)
     {