mesa: convert _NEW_RASTERIZER_DISCARD to a driver flag

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
diff --git a/src/mesa/state_tracker/st_context.c b/src/mesa/state_tracker/st_context.c
index ed1bf26..25e895b 100644
--- a/src/mesa/state_tracker/st_context.c
+++ b/src/mesa/state_tracker/st_context.c
@@ -208,6 +208,7 @@
 static void st_init_driver_flags(struct gl_driver_flags *f)
 {
    f->NewArray = ST_NEW_VERTEX_ARRAYS;
+   f->NewRasterizerDiscard = ST_NEW_RASTERIZER;
 }
 
 struct st_context *st_create_context(gl_api api, struct pipe_context *pipe,