Use `flock` instead of `fcntl` to lock files

`flock` locks based on the file handle, instead of the process id.
This brings the file locking on unix based systems closer to file
locking on Windows.
ea6525797dLeRoyce Pearson committed on 4/3/2020, 4:57:02 AMparente7cf3f9
12 files changedLine totals unavailable