Merging r201843

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r201843 | chandlerc | 2014-02-21 00:37:30 -0800 (Fri, 21 Feb 2014) | 4 lines

Teach libc++ to use the compiler-provided C-compatible ::max_align_t
rather than its own type for std::max_align_t. This is particularly
relevant as the types may not be ABI compatible despite users expecting
them to be.
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llvm-svn: 209032

libcxx/include/cstddef

@@ -52,7 +52,12 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 using ::ptrdiff_t;
 using ::size_t;
 
+#if defined(__CLANG_MAX_ALIGN_T_DEFINED) || defined(_GCC_MAX_ALIGN_T)
+// Re-use the compiler's <stddef.h> max_align_t where possible.
+using ::max_align_t;
+#else
 typedef long double max_align_t;
+#endif
 
 #ifdef _LIBCPP_HAS_NO_NULLPTR