Add a missing stdio.h include.

The code happened to compile without this include on Cygwin and MSYS2,
the original MSYS/MinGW toolchain rejects it.

src/agent/InputMap.cc

@@ -21,6 +21,7 @@
 #include "InputMap.h"
 
 #include <windows.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>