Add some debugger memory utilities (#109)

* add some memory utilities

* run waitpid in a separate thread and support very simple breakpoints

* fix breakpoints

* add missing windows stub function

* fix error message on exit

game/kernel/kmalloc.cpp

@@ -6,6 +6,7 @@
  */
 
 #include <cstring>
+#include "common/goal_constants.h"
 #include "kmalloc.h"
 #include "kprint.h"
 #include "kscheme.h"