update build file to work in 0.13.0

[lygaret]

without this change, build fails with:

 no field named 'path' in union 'Build.LazyPath'

after this change, zig build test succeeds.

This is part of two PRs, one here and one against the linenoize repo I'll open shorrtly.
I'm working on getting linenoize running under 0.13.0, for which wcwidth is a dependency.

Thank you for your help and the library!

[joachimschmidt557]

Thanks!