It writes the core of live stopped process to the file descriptor
provided as an argument.
Based on the initial version from https://reviews.freebsd.org/D29691,
submitted by Michał Górny <firstname.lastname@example.org>.
Reviewed by: markj
Tested by: pho
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D29955