Fix QNX and IRIX compilation

extra/innochecksum.c:
  Fix _XOPEN_SOURCE define to not break compile on QNX and IRIX

extra/innochecksum.c

@@ -28,7 +28,7 @@
 #define _LARGEFILE_SOURCE
 #define _LARGEFILE64_SOURCE
 
-#define _XOPEN_SOURCE /* needed to include getopt.h on some platforms. */
+#define _XOPEN_SOURCE 500 /* needed to include getopt.h on some platforms. */
 
 #include <stdio.h>
 #include <stdlib.h>