Deprecating OS support

[Paul Smith]

Hi all;

With the upcoming release (4.4) I intend to announce that I'll be
removing support for the following platforms in the next, post-4.4
release:

  - OS/2 (EMX)
  - Amiga
  - Native MS-DOS

For the first two, I suspect that whatever support we currently have is
broken and it's not really possible to build GNU make, even today, for
those platforms.  I haven't received any input from anyone using those
platforms in years and it's hard for me to believe that, with all the
changes, everything still "just works".

I'm less sure about native MS-DOS.  Maybe someone still uses this?

If anyone thinks that any of these should be preserved and I should not
announce deprecation for them, let me know.

Obviously, versions of GNU make up to and including the upcoming 4.4
would still be available for those platforms (if they work).

This would leave us with the following supported platforms, post 4.4:

  - POSIX-based systems
  - Windows
  - VMS

For VMS I haven't heard from anyone about it this release cycle so I
don't really know what the status is, but it was actively supported in
GNU make 4.3.