glsl: fix per_vertex_accumulator::fields size

49d35f3d88 moved gl_Layer/gl_ViewportIndex/gl_ViewportMask
as builtins but fields size wasn't increased.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3508
Fixes: 49d35f3d88 ("glsl: declare gl_Layer/gl_ViewportIndex/gl_ViewportMask as vs builtins")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6688>

src/compiler/glsl/builtin_variables.cpp

@@ -319,7 +319,7 @@ public:
    const glsl_type *construct_interface_instance() const;
 
 private:
-   glsl_struct_field fields[11];
+   glsl_struct_field fields[14];
    unsigned num_fields;
 };