Remove $FreeBSD$: two-line nroff pattern

Remove /^\.\\"\n\.\\"\s*\$FreeBSD\$$\n/

use .Mt to mark up email addresses consistently (part3)

PR: 191174
Submitted by: Franco Fichtner <franco at lastsummer.de>

Pull up vendor changes to mdoc(7)

This switches us to using -isoC-2011 as the symbol name which is used by
groff and mdocml. It follows the change to 4 digit years as done with
IEEE Std 1003 post-1999.

MFC after: 2 weeks (groff changes only)

Add libstdthreads.

This library implements the C11 threads interface on top of the pthreads
library. As discussed on the lists, the preferred way to implement
this, is as a separate library.

It is unlikely that these functions will be used a lot in the future. It
would have been easier if the C11 working group standardized (a subset
of) pthreads and clock_nanosleep(). Having it as a separate library
allows the embedded people to omit it from their system.

Discussed on: arch@, threads@