Add std::make_unique implementation

It's not available in C++11, it was added in C++14.

goo/gmem.h

diff --git a/goo/gmem.h b/goo/gmem.h
index 898f339..4dad2d3 100644
--- a/goo/gmem.h
+++ b/goo/gmem.h
@@ -25,6 +25,7 @@
 #ifndef GMEM_H
 #define GMEM_H
 
+#include <memory>
 #include <stdio.h>
 #include "poppler-config.h"
 
@@ -89,4 +90,37 @@
 }
 #endif
 
+/* Remove this once we switch to C++14 */
+#if __cplusplus < 201400L
+namespace std {
+template<class T> struct _Unique_if {
+  typedef unique_ptr<T> _Single_object;
+};
+
+template<class T> struct _Unique_if<T[]> {
+  typedef unique_ptr<T[]> _Unknown_bound;
+};
+
+template<class T, size_t N> struct _Unique_if<T[N]> {
+  typedef void _Known_bound;
+};
+
+template<class T, class... Args> inline typename _Unique_if<T>::_Single_object
+make_unique(Args&&... args)
+{
+  return unique_ptr<T>(new T(std::forward<Args>(args)...));
+}
+
+template<class T> inline typename _Unique_if<T>::_Unknown_bound
+make_unique(size_t n)
+{
+  typedef typename remove_extent<T>::type U;
+  return unique_ptr<T>(new U[n]());
+}
+
+template<class T, class... Args> typename _Unique_if<T>::_Known_bound
+make_unique(Args&&...) = delete;
+}
+#endif
+
 #endif