Function build_class 

pub fn build_class(
    name: &str,
    parent: Value,
    ctor: Value,
    source_def: Option<usize>,
) -> Value

Build a class constructor value from its parts. The compiler emits (via MKCLASS) the evaluated parent (or undefined) and the constructor closure (or undefined for a default constructor); methods/getters/setters/statics/fields are installed afterward by DEF_MEMBER/DEF_FIELD.