libevent: headers are not in $includedir

They are in $opalincludedir.  Use the neutral "$pkgincludedir", which
will get translated under the covers to opalincludedir.

opal/mca/event/libevent2022/configure.m4

@@ -1,6 +1,6 @@
 # -*- shell-script -*-
 #
-# Copyright (c) 2009-2013 Cisco Systems, Inc.  All rights reserved.
+# Copyright (c) 2009-2015 Cisco Systems, Inc.  All rights reserved.
 # Copyright (c) 2012-2013 Los Alamos National Security, LLC.  All rights reserved.
 # Copyright (c) 2015      Intel, Inc. All rights reserved.
 #
@@ -176,7 +176,7 @@ AC_DEFUN([MCA_opal_event_libevent2022_DO_THE_CONFIG], [
     # Finally, add some flags to the wrapper compiler if we're
     # building with developer headers so that our headers can
     # be found.
-    event_libevent2022_WRAPPER_EXTRA_CPPFLAGS='-I${includedir}/openmpi/opal/mca/event/libevent2022/libevent -I${includedir}/openmpi/opal/mca/event/libevent2022/libevent/include'
+    event_libevent2022_WRAPPER_EXTRA_CPPFLAGS='-I${pkgincludedir}/openmpi/opal/mca/event/libevent2022/libevent -I${pkgincludedir}/openmpi/opal/mca/event/libevent2022/libevent/include'
 
     CFLAGS="$CFLAGS_save"
     CPPFLAGS="$CPPFLAGS_save"