Add basic thread pool scheduling loop.

Right now no work can be spawned, we simply have a proove of concept that we start up each thread, work for the master to finish and then synchronize back to the main thread.
Status Job ID Name Coverage
  Build
passed #2689
build_cmake

00:32

 
  Test
passed #2690
run_tests

00:36

 
  Sanitizer
passed #2691
run_thread_sanitizer

00:49