bug#36927: 26.2.90; include stdarg.h is without hyperlinking on vfprintf's manpage

[Eli Zaretskii <eliz@gnu.org>]

> From: VanL <van@scratch.space>
> Date: Sat, 10 Aug 2019 15:05:16 +1000
> Cc: 36927@debbugs.gnu.org
> 
> > The logic in Man-highlight-references0 was flawed: it assumed that a
> > section ("SYNOPSIS", "FILES", "SEE ALSO", etc.) is always received
> > entirely in a single chunk of text that is read from the subprocess,
> > which is, of course, not guaranteed, and depends on factors such as
> > the size of each section, buffering, how busy is the system, etc.
> > (Those reasons also made this a bitch to debug, because a bug comes
> > and goes unpredictably, and never shows when one steps with Edebug.)
> 
> Thanks.
> 
> That sounds really convoluted and this is what I can see

The comments should explain what the code does.  Let me know which
parts are unclear.

> A possible way is to wait for all the subprocess sections to be done and to post-process on the fully collected buffer having lines like

I considered this possibility, but rejected it: since we display the
man page even before the async subprocess exits, it would mean that
the displayed portion is not fontified until the very end, which would
render the entire idea of formatting in the background useless, and
would have use behave on all platforms as we do on MS-DOS.