First set of changes to move globals to instance_globals.

include/hack.h

@@ -22,6 +22,15 @@
         0     \
     }
 
+/* The UNDEFINED macros are used to initialize variables whose
+   initialized value is not relied upon.
+   UNDEFINED_VALUE: used to initialize any scalar type except pointers.
+   UNDEFINED_VALUES: used to initialize any non scalar type without pointers.
+   UNDEFINED_PTR: can be used only on pointer types. */
+#define UNDEFINED_VALUE 0
+#define UNDEFINED_VALUES { 0 }
+#define UNDEFINED_PTR NULL
+
 /* symbolic names for capacity levels */
 enum encumbrance_types {
     UNENCUMBERED = 0,