[patch] Add const to constexpr member functions

[Jonathan Wakely]

Add const to functions that would change meaning in C++14.

Tested x86_64-linux, committed to trunk.

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commit f30d35d5a7aa3ff2e0d0e4010aecaf9f5a5fb9ed
Author: Jonathan Wakely <accu@kayari.org>
Date:   Tue Apr 15 18:55:45 2014 +0100

    	* include/bits/atomic_base.h (__atomic_base<_PTp*>::_M_type_size): Add
    	const to constexpr member functions.

diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
index 242459a..1fc0ebb 100644
--- a/libstdc++-v3/include/bits/atomic_base.h
+++ b/libstdc++-v3/include/bits/atomic_base.h
@@ -675,10 +675,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       // Factored out to facilitate explicit specialization.
       constexpr ptrdiff_t
-      _M_type_size(ptrdiff_t __d) { return __d * sizeof(_PTp); }
+      _M_type_size(ptrdiff_t __d) const { return __d * sizeof(_PTp); }
 
       constexpr ptrdiff_t
-      _M_type_size(ptrdiff_t __d) volatile { return __d * sizeof(_PTp); }
+      _M_type_size(ptrdiff_t __d) const volatile { return __d * sizeof(_PTp); }
 
     public:
       __atomic_base() noexcept = default;