prevent redefinition of offsetof on OS X
prevent redefinition of offsetof on OS X

ros2/rosidl_typesupport,esteve/rosidl_typesupport,ros2/rosidl_typesupport,ros2/rosidl,esteve/rosidl,ros2/rosidl,ros2/rosidl_typesupport,esteve/rosidl_typesupport,ros2/rosidl,esteve/rosidl_typesupport,ros2/rosidl,esteve/rosidl,esteve/rosidl