=== Linux compatibility layer update

Contact: Edward Tomasz Napierala, <trasz@FreeBSD.org>

Linuxulator improvements have been ongoing for the last two years, with support from the FreeBSD Foundation over a few distinct project grants as well as contributions from the community.
The goal of this project is to improve FreeBSD's ability to execute unmodified Linux binaries.
Current support status of specific Linux applications is being tracked at the link:https://wiki.freebsd.org/LinuxApps[Linux app status Wiki page].

The work this quarter focused on making sure the 13.0-RELEASE ships with Linuxulator in a good shape, and fixing problems reported by users.
There are some new directories provided by `linsysfs(5)`, the lack of which, through a curious chain of events, broke installation of make(1) in Ubuntu Focal.
The `getcwd(2)` syscall was fixed to no longer return the wrong error value for certain conditions, which was breaking Mono.
The `getsockopt(2)` syscall now supports `SO_PEERSEC` and `SO_PEERGROUPS`, which are being used by su(8) and sudo(8).
Other fixes include flag handling for 32-bit `send(2)` syscall, and several ptrace(2) problems, which were affecting Steam games.  The kernel version was bumped to 3.17.0 to unbreak Qt applications from Focal.
The `sysutils/debootstrap` port, and its corresponding `debootstrap` package, now correctly handle Ubuntu's GPG keys.
The debootstrap utility now installs the `mremap(2)` workaround for `apt(8)`.
This reduces the number of steps required to set up Linux chroot or jail.
Finally there have been some improvements to the startup scripts.

Sponsor: The FreeBSD Foundation
