dj(1): only include sysexits if they aren't defined

src/dj.c

@@ -22,7 +22,9 @@
 #include <stdio.h> /* fprintf(3), stderr */
 #include <stdlib.h> /* malloc(3), strtol(3), size_t */
 #include <string.h> /* memcpy(3), memmove(3), memset(3) */
-#include <sysexits.h> /* EX_OK, EX_OSERR, EX_USAGE */
+#if !defined EX_OK || !defined EX_OSERR || !defined EX_USAGE
+#	include <sysexits.h>
+#endif
 #include <unistd.h> /* close(2), getopt(3), lseek(2), read(2), write(2),
                      * optarg, optind, STDIN_FILENO, STDOUT_FILENO */
 #include <sys/stat.h> /* S_IRGRP, S_IROTH, S_IRUSR, S_IWGRP, S_IWOTH,