Index: gcc/c-family/c.opt
===================================================================
--- gcc/c-family/c.opt	(revision 214396)
+++ gcc/c-family/c.opt	(working copy)
@@ -290,11 +290,11 @@ Warn about casting functions to incompat
 Wbool-compare
 C ObjC C++ ObjC++ Var(warn_bool_compare) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall)
 Warn about boolean expression compared with an integer value different from true/false
 
 Wbuiltin-macro-redefined
-C ObjC C++ ObjC++ Warning
+C ObjC C++ ObjC++ CPP(warn_builtin_macro_redefined) Var(cpp_warn_builtin_macro_redefined) Init(1) Warning
 Warn when a built-in preprocessor macro is undefined or redefined
 
 Wc90-c99-compat
 C ObjC Var(warn_c90_c99_compat) Init(-1) Warning
 Warn about features not present in ISO C90, but present in ISO C99
Index: gcc/c-family/c-opts.c
===================================================================
--- gcc/c-family/c-opts.c	(revision 214396)
+++ gcc/c-family/c-opts.c	(working copy)
@@ -383,14 +383,10 @@ c_common_handle_option (size_t scode, co
 
       cpp_opts->warn_trigraphs = value;
       cpp_opts->warn_num_sign_change = value;
       break;
 
-    case OPT_Wbuiltin_macro_redefined:
-      cpp_opts->warn_builtin_macro_redefined = value;
-      break;
-
     case OPT_Wc___compat:
       cpp_opts->warn_cxx_operator_names = value;
       break;
 
     case OPT_Wdeprecated:
Index: libcpp/macro.c
===================================================================
--- libcpp/macro.c	(revision 214396)
+++ libcpp/macro.c	(working copy)
@@ -2697,17 +2697,16 @@ warn_of_redefinition (cpp_reader *pfile,
 
   /* Some redefinitions need to be warned about regardless.  */
   if (node->flags & NODE_WARN)
     return true;
 
-  /* Suppress warnings for builtins that lack the NODE_WARN flag.  */
-  if (node->flags & NODE_BUILTIN)
-    {
-      if (!pfile->cb.user_builtin_macro
-	  || !pfile->cb.user_builtin_macro (pfile, node))
-	return false;
-    }
+  /* Suppress warnings for builtins that lack the NODE_WARN flag,
+     unless Wbuiltin-macro-redefined.  */
+  if (node->flags & NODE_BUILTIN
+      && (!pfile->cb.user_builtin_macro
+	  || !pfile->cb.user_builtin_macro (pfile, node)))
+    return CPP_OPTION (pfile, warn_builtin_macro_redefined);
 
   /* Redefinitions of conditional (context-sensitive) macros, on
      the other hand, must be allowed silently.  */
   if (node->flags & NODE_CONDITIONAL)
     return false;
@@ -3179,18 +3178,18 @@ _cpp_create_definition (cpp_reader *pfil
       if (CPP_OPTION (pfile, warn_unused_macros))
 	_cpp_warn_if_unused_macro (pfile, node, NULL);
 
       if (warn_of_redefinition (pfile, node, macro))
 	{
-          const int reason = (node->flags & NODE_BUILTIN)
+          const int reason = ((node->flags & NODE_BUILTIN)
+			      && !(node->flags & NODE_WARN))
                              ? CPP_W_BUILTIN_MACRO_REDEFINED : CPP_W_NONE;
-	  bool warned;
 
-	  warned = cpp_pedwarning_with_line (pfile, reason,
-					     pfile->directive_line, 0,
-					     "\"%s\" redefined",
-                                             NODE_NAME (node));
+	  bool warned = 
+	    cpp_pedwarning_with_line (pfile, reason,
+				      pfile->directive_line, 0,
+				      "\"%s\" redefined", NODE_NAME (node));
 
 	  if (warned && node->type == NT_MACRO && !(node->flags & NODE_BUILTIN))
 	    cpp_error_with_line (pfile, CPP_DL_NOTE,
 				 node->value.macro->line, 0,
 			 "this is the location of the previous definition");
Index: libcpp/directives.c
===================================================================
--- libcpp/directives.c	(revision 214396)
+++ libcpp/directives.c	(working copy)
@@ -608,10 +608,15 @@ do_undef (cpp_reader *pfile)
       if (node->type == NT_MACRO)
 	{
 	  if (node->flags & NODE_WARN)
 	    cpp_error (pfile, CPP_DL_WARNING,
 		       "undefining \"%s\"", NODE_NAME (node));
+	  else if ((node->flags & NODE_BUILTIN)
+		   && CPP_OPTION (pfile, warn_builtin_macro_redefined))
+	    cpp_warning_with_line (pfile, CPP_W_BUILTIN_MACRO_REDEFINED,
+				   pfile->directive_line, 0,
+				   "undefining \"%s\"", NODE_NAME (node));
 
 	  if (CPP_OPTION (pfile, warn_unused_macros))
 	    _cpp_warn_if_unused_macro (pfile, node, NULL);
 
 	  _cpp_free_definition (node);
Index: libcpp/init.c
===================================================================
--- libcpp/init.c	(revision 214396)
+++ libcpp/init.c	(working copy)
@@ -465,12 +465,11 @@ cpp_init_special_builtins (cpp_reader *p
   for (b = builtin_array; b < builtin_array + n; b++)
     {
       cpp_hashnode *hp = cpp_lookup (pfile, b->name, b->len);
       hp->type = NT_MACRO;
       hp->flags |= NODE_BUILTIN;
-      if (b->always_warn_if_redefined
-          || CPP_OPTION (pfile, warn_builtin_macro_redefined))
+      if (b->always_warn_if_redefined)
 	hp->flags |= NODE_WARN;
       hp->value.builtin = (enum cpp_builtin_type) b->value;
     }
 }