Rustc file lock not working on WSL

[nbdd0121]

WSL1 does not support fcntl-based advisory locks, therefore the current src/librustc_data_structures/flock.rs implementation does not work.

This issue can be observed by running cargo doc on a repository with many crates. The search-index.js can miss crates.

According to my test libc::flock is working on WSL. We could replace fcntl based lock with flock based lock for Linux. However this will break lock over NFS for Linux 2.6.11 or earlier, I can author a PR if that's okay.

Related WSL issue: microsoft/WSL#1927

[cuviper]

However this will break lock over NFS for Linux 2.6.11 or earlier

The minimum platform support is Linux 2.6.18, so that seems fine. If we can get away with switching all unix hosts to flock, even better.

[nbdd0121]

The minimum platform support is Linux 2.6.18, so that seems fine.

Cool.

If we can get away with switching all unix hosts to flock, even better.

Sure.