[build2] Crash on Windows v0.6.1

[Boris Kolpackov]

Klaim - Joël Lamotte <mjklaim at gmail.com> writes:

> I am back on getting back on experimenting with build2 and I was
> trying to re-do the tutorial but hit an assert violation.

We've fixed quite a bit of stuff for the next release and I suspect
this one is fixed as well. Could you re-try this with the latest
staged toolchain:

https://stage.build2.org/0/

Thanks,
Boris