glsl: pass disable_varying_packing bool to the lowering pass

This will allow us to choose to ignore the disable which will be
useful for more fine grained control over when to enable or disable
packing.

Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/compiler/glsl/ir_optimization.h

@@ -124,7 +124,8 @@ void lower_shared_reference(struct gl_shader *shader, unsigned *shared_size);
 void lower_ubo_reference(struct gl_shader *shader);
 void lower_packed_varyings(void *mem_ctx,
                            unsigned locations_used, ir_variable_mode mode,
-                           unsigned gs_input_vertices, gl_shader *shader);
+                           unsigned gs_input_vertices, gl_shader *shader,
+                           bool disable_varying_packing);
 bool lower_vector_insert(exec_list *instructions, bool lower_nonconstant_index);
 bool lower_vector_derefs(gl_shader *shader);
 void lower_named_interface_blocks(void *mem_ctx, gl_shader *shader);