glsl: redeclare built-in variable with separate shader
according to : https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_separate_shader_objects.gles.txt properly handle the declaration of these interface block varibales
Signed-off-by: cheyang cheyang@bytedance.com
Reviewed-by: Tapani Pälli tapani.palli@intel.com