i965: add support for cached shaders with xfb qualifiers

For now this disables the shader cache when transform feedback is
enabled via the GL API as we don't currently allow for it when
generating the sha for the shader.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_disk_cache.c

@@ -250,6 +250,14 @@ brw_disk_cache_upload_program(struct brw_context *brw, gl_shader_stage stage)
    if (prog == NULL)
       return false;
 
+   /* FIXME: For now we don't read from the cache if transform feedback is
+    * enabled via the API. However the shader cache does support transform
+    * feedback when enabled via in shader xfb qualifiers.
+    */
+   if (prog->sh.LinkedTransformFeedback &&
+       prog->sh.LinkedTransformFeedback->api_enabled)
+      return false;
+
    if (prog->sh.data->LinkStatus != linking_skipped)
       goto fail;