2012-10-09  Andrew MacLeod  <amacleod@redhat.com>

	PR libstdc++/54861
	* include/bits/atomic_base.h (atomic_signal_fence): Call
	__atomic_signal_fence instead of __atomic_thread_fence.

Index: include/bits/atomic_base.h
===================================================================
*** include/bits/atomic_base.h	(revision 192254)
--- include/bits/atomic_base.h	(working copy)
*************** _GLIBCXX_BEGIN_NAMESPACE_VERSION
*** 74,80 ****
  
    inline void
    atomic_signal_fence(memory_order __m) noexcept
!   { __atomic_thread_fence(__m); }
  
    /// kill_dependency
    template<typename _Tp>
--- 74,80 ----
  
    inline void
    atomic_signal_fence(memory_order __m) noexcept
!   { __atomic_signal_fence(__m); }
  
    /// kill_dependency
    template<typename _Tp>