Index: libstdc++-v3/libsupc++/guard.cc
===================================================================
--- libstdc++-v3/libsupc++/guard.cc	(revision 176310)
+++ libstdc++-v3/libsupc++/guard.cc	(working copy)
@@ -35,6 +35,7 @@
     && defined(_GLIBCXX_ATOMIC_BUILTINS_4) && defined(_GLIBCXX_HAVE_LINUX_FUTEX)
 # include <climits>
 # include <syscall.h>
+# include <unistd.h>
 # define _GLIBCXX_USE_FUTEX
 # define _GLIBCXX_FUTEX_WAIT 0
 # define _GLIBCXX_FUTEX_WAKE 1
Index: libstdc++-v3/testsuite/17_intro/headers/c++1998/49745.cc
===================================================================
--- libstdc++-v3/testsuite/17_intro/headers/c++1998/49745.cc	(revision 0)
+++ libstdc++-v3/testsuite/17_intro/headers/c++1998/49745.cc	(revision 0)
@@ -0,0 +1,22 @@
+// { dg-do compile { target *-*-linux* } }
+
+// Copyright (C) 2011 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// libstdc++/49745
+#include <iostream>
+int truncate = 0;
Index: libstdc++-v3/acinclude.m4
===================================================================
--- libstdc++-v3/acinclude.m4	(revision 176310)
+++ libstdc++-v3/acinclude.m4	(working copy)
@@ -3155,6 +3155,22 @@
   ac_save_CXXFLAGS="$CXXFLAGS"
   CXXFLAGS="$CXXFLAGS -fno-exceptions -I${toplevel_srcdir}/gcc"
 
+  AC_MSG_CHECKING([check whether it can be safely assumed that mutex_timedlock is available])
+
+  AC_TRY_COMPILE([#include <unistd.h>],
+    [
+      #if !defined(_POSIX_TIMEOUTS) || _POSIX_TIMEOUTS < 0
+      #error
+      #endif
+    ], [ac_gthread_use_mutex_timedlock=1], [ac_gthread_use_mutex_timedlock=0])
+
+  AC_DEFINE_UNQUOTED(_GTHREAD_USE_MUTEX_TIMEDLOCK, $ac_gthread_use_mutex_timedlock,
+                     [Define to 1 if mutex_timedlock is available.])
+
+  if test $ac_gthread_use_mutex_timedlock = 1 ; then res_mutex_timedlock=yes ;
+  else res_mutex_timedlock=no ; fi
+  AC_MSG_RESULT([$res_mutex_timedlock])
+
   target_thread_file=`$CXX -v 2>&1 | sed -n 's/^Thread model: //p'`
   case $target_thread_file in
     posix)
@@ -3163,7 +3179,10 @@
 
   AC_MSG_CHECKING([for gthreads library])
 
-  AC_TRY_COMPILE([#include "gthr.h"],
+  AC_TRY_COMPILE([
+                  #include "gthr.h"
+		  #include <unistd.h>
+                 ],
     [
       #ifndef __GTHREADS_CXX0X
       #error
Index: gcc/gthr-posix.h
===================================================================
--- gcc/gthr-posix.h	(revision 176310)
+++ gcc/gthr-posix.h	(working copy)
@@ -1,7 +1,7 @@
 /* Threads compatibility routines for libgcc2 and libobjc.  */
 /* Compile this one with gcc.  */
 /* Copyright (C) 1997, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007,
-   2008, 2009, 2010 Free Software Foundation, Inc.
+   2008, 2009, 2010, 2011 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -39,8 +39,17 @@
 #endif
 
 #include <pthread.h>
-#include <unistd.h>
 
+#if ((defined(_LIBOBJC) || defined(_LIBOBJC_WEAK)) \
+     || !defined(_GTHREAD_USE_MUTEX_TIMEDLOCK))
+# include <unistd.h>
+# if defined(_POSIX_TIMEOUTS) && _POSIX_TIMEOUTS >= 0
+#  define _GTHREAD_USE_MUTEX_TIMEDLOCK 1
+# else
+#  define _GTHREAD_USE_MUTEX_TIMEDLOCK 0
+# endif
+#endif
+
 typedef pthread_t __gthread_t;
 typedef pthread_key_t __gthread_key_t;
 typedef pthread_once_t __gthread_once_t;
@@ -100,11 +109,9 @@
 
 __gthrw3(pthread_mutex_lock)
 __gthrw3(pthread_mutex_trylock)
-#ifdef _POSIX_TIMEOUTS
-#if _POSIX_TIMEOUTS >= 0
+#if _GTHREAD_USE_MUTEX_TIMEDLOCK
 __gthrw3(pthread_mutex_timedlock)
 #endif
-#endif /* _POSIX_TIMEOUTS */
 __gthrw3(pthread_mutex_unlock)
 __gthrw3(pthread_mutex_init)
 __gthrw3(pthread_mutex_destroy)
@@ -131,11 +138,9 @@
 
 __gthrw(pthread_mutex_lock)
 __gthrw(pthread_mutex_trylock)
-#ifdef _POSIX_TIMEOUTS
-#if _POSIX_TIMEOUTS >= 0
+#if _GTHREAD_USE_MUTEX_TIMEDLOCK
 __gthrw(pthread_mutex_timedlock)
 #endif
-#endif /* _POSIX_TIMEOUTS */
 __gthrw(pthread_mutex_unlock)
 __gthrw(pthread_mutex_init)
 __gthrw(pthread_mutex_destroy)
@@ -753,8 +758,7 @@
     return 0;
 }
 
-#ifdef _POSIX_TIMEOUTS
-#if _POSIX_TIMEOUTS >= 0
+#if _GTHREAD_USE_MUTEX_TIMEDLOCK
 static inline int
 __gthread_mutex_timedlock (__gthread_mutex_t *__mutex,
 			   const __gthread_time_t *__abs_timeout)
@@ -765,7 +769,6 @@
     return 0;
 }
 #endif
-#endif
 
 static inline int
 __gthread_mutex_unlock (__gthread_mutex_t *__mutex)
@@ -811,8 +814,7 @@
   return __gthread_mutex_trylock (__mutex);
 }
 
-#ifdef _POSIX_TIMEOUTS
-#if _POSIX_TIMEOUTS >= 0
+#if _GTHREAD_USE_MUTEX_TIMEDLOCK
 static inline int
 __gthread_recursive_mutex_timedlock (__gthread_recursive_mutex_t *__mutex,
 				     const __gthread_time_t *__abs_timeout)
@@ -820,7 +822,6 @@
   return __gthread_mutex_timedlock (__mutex, __abs_timeout);
 }
 #endif
-#endif
 
 static inline int
 __gthread_recursive_mutex_unlock (__gthread_recursive_mutex_t *__mutex)