Added nhassert to core.

include/global.h

@@ -375,5 +375,10 @@ struct savefile_info {
 #define nethack_enter(argc, argv) ((void) 0)
 #endif
 
+/* Supply nhassert macro if not supplied by port */
+#ifndef nhassert
+#define nhassert(expression) (void)((!!(expression)) || \
+        (nhassert_failed(#expression, __FILE__, __LINE__), 0))
+#endif
 
 #endif /* GLOBAL_H */