MFC r314942:

Import the awk(1) manpage from OpenBSD

As discussed during AsiaBSDcon devsummit, import the manpage from OpenBSD which
is has been rewritten in mdoc(7) format making it readable by default with
mandoc, it also has been extended by OpenBSD to cover all awk(1) options

Obtained from: OpenBSD
MFC: 1 week