xorg/st: fixup builds against later dpms headers.
diff --git a/configure.ac b/configure.ac
index 7518976..2881bb6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1148,6 +1148,11 @@
         if test "$tracker" = egl && test "x$enable_egl" != xyes; then
             AC_MSG_ERROR([cannot build egl state tracker without EGL library])
         fi
+        if test "$tracker" = xorg; then
+	    PKG_CHECK_MODULES(XEXT, [xextproto >= 7.0.99.1],
+                  HAVE_XEXTPROTO_71="yes"; DEFINES="$DEFINES -DHAVE_XEXTPROTO_71"
+                  HAVE_XEXTPROTO_71="no")
+	fi
     done
     GALLIUM_STATE_TRACKERS_DIRS="$state_trackers"
     ;;