Feature or enhancement

Expose PIDFD_NONBLOCK as os.PIDFD_NONBLOCK to be used with os.waitid.

Pitch

pidfd_open returns a nonblocking file descriptor if PIDFD_NONBLOCK is supplied as flag. If the process
referred to by the file descriptor has not yet terminated,
then an attempt to wait on the file descriptor using
waitid(2) will immediately return the error EAGAIN rather
than blocking.

Linked PRs

• gh-93312: Include <sys/pidfd.h> to get PIDFD_NONBLOCK #127593
• [3.13] gh-93312: Include <sys/pidfd.h> to get PIDFD_NONBLOCK (GH-127593) #127630
• [3.12] gh-93312: Include <sys/pidfd.h> to get PIDFD_NONBLOCK (#127593) #127631