Put std::piecewise_construct_t back into the dylib for ABI stability.  When clients are in C++11/constexpr mode this will be safely ignored because piecewise_construct is then declared with internal linkage.

llvm-svn: 153981
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 7e5b4c932850a0cf28c6439b6f3045eb53e47a5c
diff --git a/src/utility.cpp b/src/utility.cpp
index deb5ffa..e9830e7 100644
--- a/src/utility.cpp
+++ b/src/utility.cpp
@@ -7,12 +7,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+#define _LIBCPP_BUILDING_UTILITY
 #include "utility"
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#ifdef _LIBCPP_HAS_NO_CONSTEXPR
 const piecewise_construct_t piecewise_construct = {};
-#endif
 
 _LIBCPP_END_NAMESPACE_STD