Lockfile will warn periodically if waiting more than 5s

[league]

Fixes #232.

I think this is ready to go. There's a self-contained test program at the bottom of the file, it's easy to compile and test in isolation.

Is a cerr message good enough?

[league]

I will add the PID check to this PR.

[jaycedowell]

Works for me on Ubuntu 20.04 and MacOS 12.7.

[jaycedowell]

I was about to merge this when I noticed that the self-hosted builds were hanging. Why's that happening?

[jaycedowell]

Self hosted is back.