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

[VanL <van@scratch.space>]

> On 10 Aug 2019, at 17:48, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> 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.

Graphics engines use a two buffer mechanism for collecting unfinished pixels backstage in one buffer and displaying finished pixels on stage in the ready buffer and then they alternate in their role.  Not having all the `#include' lines buttonized is like missing a main character on stage.  Of the 40 `(defun' signatures in man.el the following 6 hint of opportunities in the event model's pipeline to place buttons in at 

  2) `update' or 6) `cleanup' before 3) `notify-when-ready'

1) on line 1075: (defun Man-getpage-in-background (topic)
2) on line 1127: (defun Man-update-manpage ()
3) on line 1154: (defun Man-notify-when-ready (man-buffer)
4) on line 1262: (defun Man-highlight-references (&optional xref-man-type)
5) on line 1289: (defun Man-highlight-references0 (start-section regexp button-pos target type)
6) on line 1331: (defun Man-cleanup-manpage (&optional interactive)