Add missing <errno.h>

This commit was SVN r1604.

src/tools/openmpi/openmpi.c

@@ -11,6 +11,7 @@ openmpi.c - main program for spawning persistent universe.
 
 #include <stdio.h>
 #include <string.h>
+#include <errno.h>
 
 #include "ompi_config.h"