Fix the --disable-dlopen case -- don't expect to build or link anything.

This commit was SVN r23198.

opal/config/opal_setup_libltdl.m4

@@ -40,6 +40,8 @@ AC_DEFUN([OPAL_SETUP_LIBLTDL],[
 
     AS_IF([test "$OPAL_ENABLE_DLOPEN_SUPPORT" = "0"],
           [AC_MSG_WARN([libltdl support disabled (by --disable-dlopen)])
+           LIBLTDL=
+           LDTLINCL=
            WRAPPER_EXTRA_LIBS="$WRAPPER_EXTRA_LIBS $LIBS"],
           [
            # Default to building the internal copy.  After this,