llvmpipe: fill in debug vertex info for tri rasterization

This is pretty useful for debugging rasterization issues, so turn it on
based on DEBUG (the actual existence of the fields is also conditionalized
on DEBUG, lines fill it out the same too).

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

src/gallium/drivers/llvmpipe/lp_setup_tri.c

@@ -358,7 +358,7 @@ do_triangle_ccw(struct lp_setup_context *setup,
    if (!tri)
       return FALSE;
 
-#if 0
+#ifdef DEBUG
    tri->v[0][0] = v0[0][0];
    tri->v[1][0] = v1[0][0];
    tri->v[2][0] = v2[0][0];