Don't wrap system headers with extern "C"

gcc/config/i386/nacl.h

 /* Target definitions for GCC for NativeClient using ELF
    Copyright (C) 1988, 1991, 1995, 2000, 2001, 2002
    Free Software Foundation, Inc.
 
    Derived from sysv4.h written by Ron Guilmette (rfg@netcom.com).
 
 This file is part of GCC.
 
 GCC is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
@@ skipping 19 matching lines @@
 #ifdef IN_TARGET_LIBS
 #undef BIGGEST_FIELD_ALIGNMENT
 #define BIGGEST_FIELD_ALIGNMENT 128
 #endif
 
 /* These definitions modify those in i386elf.h. */
 
 #undef TARGET_VERSION
 #define TARGET_VERSION fprintf (stderr, " (NativeClient)");
 
+/* Don't enclose system header files in extern "C" {...}.  */
+#define NO_IMPLICIT_EXTERN_C
+
 /* Provide a STARTFILE_SPEC.  Here we add
    the GNU/Linux magical crtbegin.o file (see crtstuff.c) which provides part of
    the support for getting C++ file-scope static object constructed before
    entering `main'.  */
    
 #undef  STARTFILE_SPEC
 #if defined HAVE_LD_PIE
 #define STARTFILE_SPEC \
   "%{!shared: %{pg|p|profile:gcrt1.o%s;pie:Scrt1.o%s;:crt1.o%s}} \
    crti.o%s %{static:crtbeginT.o%s;shared|pie:crtbeginS.o%s;:crtbegin.o%s}"
@@ skipping 239 matching lines @@
 #undef TARGET_USE_BT
 #define TARGET_USE_BT           (ix86_tune_features[X86_TUNE_USE_BT] && !TARGET_NACL)
 
 #undef DBX_REGISTER_NUMBER
 #define DBX_REGISTER_NUMBER(n) \
   (TARGET_64BIT ? dbx64_register_map[n] : svr4_dbx_register_map[n])
 
 #define DWARF2_ADDR_SIZE \
     (TARGET_NACL ? (TARGET_64BIT ? 8 : 4) : \
                    (POINTER_SIZE / BITS_PER_UNIT))