bug#51658: [PATCH] Haiku port (again)

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 07 Nov 2021 19:29:32 +0800
> From:  Po Lu via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> OK, after using this port for more than a month now I can say it's
> finally stable enough for heavy use.
> 
> I think all the major bugs have been ironed out now, so I'm submitting
> it for inclusion.
> 
> I couldn't figure out how to turn multiple (hundereds) of git commits
> into a single patch formatted like `git format-patch' would, so I
> attached the output of `git diff' instead.
> 
> Please take some time to review the code and possibly install it.

Thanks.

It's a large patch, so let's start with the general, a.k.a. "big"
aspects.

First, do we really need to use *.cc files and compile with a C++
compiler?  Is that a necessity?  AFAICT, the code in those *.cc files
is plain C, so why not use a C compiler, as we do on every other
platform?

Next, the font backend stuff: do we really need 5 (five) backends?
How about having just one: HarfBuzz+Cairo?  That's the direction we go
on other platforms, so how about making the Haiku code smaller and
simpler and support just that single backend, and drop all the older
ones?  I'd definitely won't want to drag the unmaintained libm17n-flt
into this port.

If you are okay with the above, could you please update the patch, so
that we could avoid reviewing code which eventually won't be
installed?