debug.h will now work standalone

src/debug.h

@@ -2,6 +2,11 @@
 #define _fencer_debug_h
 
 #include <stdio.h>
+#include <stdlib.h>
+
+#ifndef NDEBUG
+#include <assert.h>
+#endif
 
 extern int g_debug_error_abort;
 extern int g_debug_log_lvl;