Add a new member to the end of a struct/union.
arg1 The type name of the struct/union (parent).
arg2 The type of the new member.
arg3 The name of the new member.
[arg4] The array size. A value greater than zero will make this member an array.
[arg5] Offset from the start of the structure, only use this for implicitly padded structures. Overlapping with other members is not allowed.
This command does not set any result variables.