Fix build error when chibi scheme not present

src/debug.c

@@ -34,6 +34,7 @@
 #include "little_endian.h"
 #include "xsystem4.h"
 
+bool dbg_enabled = true;
 static jmp_buf dbg_continuation;
 
 enum {

src/debugger_scm.c

@@ -31,8 +31,6 @@
 #include "debugger.h"
 #include "little_endian.h"
 
-bool dbg_enabled = true;
-
 struct variable {
 	enum ain_data_type data_type;
 	int struct_type;

src/util.c

@@ -17,6 +17,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
+#include <ctype.h>
 
 #include "system4.h"
 #include "system4/utfsjis.h"