silence warning on solaris 10

use HAVE_STRINGS_H to protect <strings.h> include

cmr=v1.8.2:reviewer=rhc:ticket=trac:4853

This commit was SVN r32510.

The following Trac tickets were found above:
  Ticket 4853 --> https://svn.open-mpi.org/trac/ompi/ticket/4853

opal/class/opal_value_array.h

@@ -22,7 +22,9 @@
 #include "opal_config.h"
 
 #include <string.h>
+#ifdef HAVE_STRINGS_H
 #include <strings.h>
+#endif /* HAVE_STRINGS_H */
 
 #include "opal/class/opal_object.h"
 #if OPAL_ENABLE_DEBUG