Fixes #544

Including `<iostream>` allows LDC to compile correctly on some Macs running OS X Mavericks.

Author: itaiferber

gen/logger.h

@@ -16,6 +16,7 @@
 #define LDC_GEN_LOGGER_H
 
 #include <iosfwd>
+#include <iostream>
 
 namespace llvm {
     class Type;