mesa: Add a flag to indicate whether a program uses gl_ClipDistance.

GLSL 1.30 requires us to use gl_ClipDistance for clipping if the
vertex shader contains a static write to it, and otherwise use
user-defined clipping planes.  Since the driver needs to behave
differently in these two cases, we need a flag to record whether the
shader has written to gl_ClipDistance.

The new flag is called UsesClipDistance.  We initially store it in
gl_shader_program (since that is the data structure that is available
when we check to see whethe gl_ClipDistance was written to), and we
later copy it to a flag with the same name in gl_vertex_program, since
that is a more convenient place for the driver to access it (in i965,
at least).

Reviewed-by: Eric Anholt <eric@anholt.net>
Tested-by: Brian Paul <brianp@vmware.com>

src/mesa/program/ir_to_mesa.cpp

@@ -3291,6 +3291,8 @@ _mesa_ir_link_shader(struct gl_context *ctx, struct gl_shader_program *prog)
 
          switch (prog->_LinkedShaders[i]->Type) {
          case GL_VERTEX_SHADER:
+            ((struct gl_vertex_program *)linked_prog)->UsesClipDistance
+               = prog->Vert.UsesClipDistance;
             _mesa_reference_vertprog(ctx, &prog->VertexProgram,
                                      (struct gl_vertex_program *)linked_prog);
             ok = ctx->Driver.ProgramStringNotify(ctx, GL_VERTEX_PROGRAM_ARB,