tests: opendir-tst1: add header for mknod()

Include sys/stat.h for mknod() prototype.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

test/misc/opendir-tst1.c

@@ -24,6 +24,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <sys/stat.h>
 
 /* Name of the FIFO.  */
 char tmpname[] = "fifoXXXXXX";