core: placement new requires #include <new>, fixing that and a few other

missing includes.

src/real.cpp

@@ -12,8 +12,11 @@
 #   include "config.h"
 #endif
 
+#include <new>
 #include <cstring>
 #include <cstdio>
+#include <cstdlib>
+#include <cmath>
 
 #include "core.h"