make: fix GCC warnings

@@ -30,12 +30,12 @@
 extern void     append_char(wchar_t from, register String to);
 extern Property append_prop(register Name target, register Property_id type);
 extern void     append_string(register wchar_t *from, register String to, register int length);
 extern void     enable_interrupt(register void (*handler) (int));
 extern char     *errmsg(int errnum);
-extern void     fatal_mksh(char * message, ...);
-extern void     fatal_reader_mksh(char * pattern, ...);
+extern void     fatal_mksh(const char *message, ...);
+extern void     fatal_reader_mksh(const char *pattern, ...);
 extern char     *get_current_path_mksh(void);
 extern Property get_prop(register Property start, register Property_id type);
 extern char     *getmem(register int size);
 extern Name     getname_fn(wchar_t *name, register int len, register Boolean dont_enter, register Boolean * foundp = NULL);
 extern void     store_name(Name name);