glsl: pass UseSTD430AsDefaultPacking to where it will be used

Here we also make use of the UseSTD430AsDefaultPacking constant
and call the new get_internal_ifc_packing() helper.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/compiler/glsl/link_varyings.cpp

@@ -1843,7 +1843,7 @@ public:
 
       this->toplevel_var = var;
       this->varying_floats = 0;
-      program_resource_visitor::process(var);
+      program_resource_visitor::process(var, false);
    }
 
 private: