vl: Add switches to autoconf.

Pass 'xorg/xvmc' to --with-state-trackers to get the XvMC state tracker.
Pass --enable-gallium-g3dvl to enable the winsys.
diff --git a/configure.ac b/configure.ac
index f9476a4..bc2d5c1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1241,6 +1241,22 @@
     GALLIUM_DRIVERS_DIRS="$GALLIUM_DRIVERS_DIRS nouveau nv04 nv10 nv20 nv30 nv40 nv50"
 fi
 
+dnl
+dnl Gallium G3DVL configuration
+dnl
+AC_ARG_ENABLE([gallium-g3dvl],
+    [AS_HELP_STRING([--enable-gallium-g3dvl],
+        [build gallium g3dvl @<:@default=disabled@:>@])],
+    [enable_gallium_g3dvl="$enableval"],
+    [enable_gallium_g3dvl=no])
+if test "x$enable_gallium_g3dvl" = xyes; then
+    vl_winsys_dirs=""
+    for dir in $GALLIUM_WINSYS_DIRS; do
+        vl_winsys_dirs="$vl_winsys_dirs g3dvl/$dir"
+    done
+    GALLIUM_WINSYS_DIRS="$GALLIUM_WINSYS_DIRS $vl_winsys_dirs"
+fi
+
 
 dnl Restore LDFLAGS and CPPFLAGS
 LDFLAGS="$_SAVE_LDFLAGS"