toxvpn fails to build against toxcore from irungentoo's repo

[msva]

Currently, toxvpn fails to build against toxcore from that overlay.
The reason is:

• toxcore package using https://github.com/irungentoo/toxcore (and even a bit outdated "master" branch, while development is moved to the "new" branch.
• toxvpn is developing against https://github.com/TokTok/c-toxcore fork