New port: lang/myrddin

Myrddin is a systems programming language that covers a similar niche
as C including desktop, OS, and embedded development, but at the same
time making it harder to shoot yourself in the foot.

It is designed to be a simple language that runs close to the metal,
giving the programmer predictable and transparent behavior and mental
model.  It also does strong type checking, generics, type inference,
closures, and traits.

Myrddin is not a language designed to explore the forefront of type
theory or compiler technology.  It is not a language that is focused
on guaranteeing perfect safety.  It is satisfied to be a practical,
small, fairly well defined, and easy to understand language for code
that needs to be close to the hardware.

WWW: https://myrlang.org/

Approved by:	??? (mentor)
Differential Revision:	https://reviews.freebsd.org/D????