NGI project: https://nlnet.nl/project/RedoxOS-Signals/

The goal of this milestone is to move signal handling to userspace, except for a small generalized kernel part. This has been almost fully achieved on the implementation side, but TODO the test suite subproject.

• Move signal handling (sigprocmask and sigaction) to userspace, with basic ability to catch, ignore, suspend, restart or terminate processes
• Implement syscall restarting in relibc
• Modify key drivers and servies to allow requests to be canceled
• Implement signal queueing (realtime signals), initially in the kernel, and implement all remaining signal-related POSIX APIs
• Pass basic functional tests at the process level for all signals functions