Don't use #pragma; don't redefine make_unique if using C++14

include/stdshims.h

@@ -1,14 +1,17 @@
 //! Shims for std:: functions that aren't available in the current C++ versions
 //! we target.
 
-#pragma once
+#ifndef STDSHIMS_H
+#define STDSHIMS_H
 
 #include <memory>
 #include <utility>
 
 #if (__cplusplus >= 201402L)
 #warning "This file should now be removed! The functions it provides are part of the C++14 standard."
-#endif
+using std::unique_ptr;
+
+#else
 
 /// Shim for http://en.cppreference.com/w/cpp/memory/unique_ptr/make_unique
 template<typename T, typename... Args>
@@ -16,4 +19,7 @@ std::unique_ptr<T> make_unique(Args&&... args)
 {
 	return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
 }
+#endif
+
+#endif // include guard