includes/std: Added missing mem library include in ptr libary

includes/std/ptr.pat

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <std/mem.pat>
+
 /*!
     The Pointer library contains helper functions to deal with pointer types.
     The `relative_to` functions are meant to be used with the `[[pointer_base]]` attribute
@@ -64,4 +66,4 @@ namespace std::ptr {
             PointeeTy *data : PointerTy;
         }
     };
-}
+}