nir/linking: fix issue with two compact variables in a row. (v2)

If we have a clip dist float[1] compact followed by a tess factor
float[2] we don't want to overlap them, but the partial check
only happens for non-compact vars.

This fixes some issues seen with my sw vulkan layer with
dEQP-VK.clipping.user_defined.clip_distance*

v2: v1 failed with clip/cull mixtures, since in that
case the cull has a location_frac to follow after the clip
so only reset if we get a location_frac of 0 in a subsequent
clip var

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4635>

src/compiler/nir/nir_linking_helpers.c

@@ -1113,6 +1113,14 @@ nir_assign_io_var_locations(struct exec_list *var_list, unsigned *size,
 
       unsigned var_size;
       if (var->data.compact) {
+         /* If we are inside a partial compact,
+          * don't allow another compact to be in this slot
+          * if it starts at component 0.
+          */
+         if (last_partial && var->data.location_frac == 0) {
+            location++;
+         }
+
          /* compact variables must be arrays of scalars */
          assert(glsl_type_is_array(type));
          assert(glsl_type_is_scalar(glsl_get_array_element(type)));