Add illumos to build constraints

[szaydel]

This small change enables building this code, and by extension promtail on illumos-based systems. Thank you in advance for considering this change.

Regards, Sam.

[CLAassistant]

All committers have signed the CLA.

[szaydel]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.You have signed the CLA already but the status is still pending? Let us recheck it.

I would love to sign the CLA, but this is all I am seeing when I attempt to do it.

[szaydel]

I think today it is actually working and I signed the CLA. Hopefully that's enough to move this forward.

[szaydel]

Just wanted to bump this PR and see if there is anything standing in the way. This would really help with adoption on illumos-based systems.

Thanks!

[szaydel]

Please let me know if I should withdraw this PR. It is now a much larger change than what it was initially. The problem is with the fsnotify package. Unfortunately, upstream has not yet released a version which has the necessary FEN support, which required the changes introduced in ed110e2. If this is unacceptable for the project, please let me know and we can close out this PR.

Thank you, Sam.