--- a/gcc/config/mmix/mmix.h	Fri Oct 27 22:46:09 2017 +0900
+++ b/gcc/config/mmix/mmix.h	Thu Oct 25 07:37:49 2018 +0900
@@ -1,5 +1,5 @@
 /* Definitions of target machine for GNU compiler, for MMIX.
-   Copyright (C) 2000-2017 Free Software Foundation, Inc.
+   Copyright (C) 2000-2018 Free Software Foundation, Inc.
    Contributed by Hans-Peter Nilsson (hp@bitrange.com)
 
 This file is part of GCC.
@@ -761,7 +761,7 @@
 /* (empty) */
 
 
-/* Node: SDB and DWARF */
+/* Node: DWARF */
 #define DWARF2_DEBUGGING_INFO 1
 #define DWARF2_ASM_LINE_DEBUG_INFO 1
 
@@ -789,8 +789,6 @@
 
 #define FUNCTION_MODE QImode
 
-#define NO_IMPLICIT_EXTERN_C
-
 /* mmix-knuth-mmixware target has no support of C99 runtime */
 #undef TARGET_LIBC_HAS_FUNCTION
 #define TARGET_LIBC_HAS_FUNCTION no_c99_libc_has_function