util.signal: Fail signalfd() if unable to change signal mask
By aborting early, the failure should be brought to the attention
somehow.
For full information on our dependencies, version requirements, and
where to find them, see https://prosody.im/doc/depends
If you have luarocks available on your platform, install the following:
- luaexpat
- luasocket
- luafilesystem
- luasec