Update: Implement threaded signal handler in Featureless Make.

Update: Implement threaded signal handler in Featureless Make.

Bring in the threaded signal handler design that I experimented with in the Kevux Tools project.

This works by creating a thread that waits for the signal and nothing else.
The threaded design avoids the signal check and therefore avoids period calls to kernel space.

When thread support is diabled, this falls back to the traditional approach.

This will be done for other programs as well.