draw/llvm: add clip distance support

draw/llvm: add clip distance support

This add clipdistance support like the non-llvm draw paths,
if we have a clip distance we compare with it instead of doing
the dot4.

We also have to put the have_clipvertex bit into the emitted
vertex header.

Fixes vs-clip-distance-all-planes-enabled, vs-clip-distance-const-reject,
vs-clip-distance-enables, vs-clip-distance-implicitly-sized,
vs-clip-distance-in-param, vs-clip-distance-uint-index.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Brian Paul <brianp@vmware.com>