Missing include file when this is "included" by itself

This commit was SVN r13192.

opal/runtime/opal.h

@@ -21,6 +21,8 @@
 #ifndef OPAL_H
 #define OPAL_H
 
+#include "opal_config.h"
+
 #if defined(c_plusplus) || defined(__cplusplus)
 extern "C" {
 #endif