[lmi] Advance note about a change to MinGW packages in Debian

[Vadim Zeitlin]

 Hello,

 Let me start by saying that there is nothing that needs to be done about
this right now, but I just wanted to let you know about the following
message I got from apt-listchanges when upgrading one of my Debian systems:

---------------------------------- >8 --------------------------------------
gcc-mingw-w64 (25) unstable; urgency=medium

    The sets of packages for POSIX and Win32 thread models are no longer
    co-installable; the appropriate thread model must now be chosen at
    installation time, not using alternatives.

 -- Stephen Kitt <skitt@debian.org>  Mon, 12 Dec 2022 08:50:30 +0100
---------------------------------- >8 --------------------------------------

 And, indeed, the "-win32" and "-posix" versions of the various MinGW
packages can't be installed together any longer: by default, the "-win32"
variant is installed and if you install "-posix" one manually later, the
"-win32" one is removed.

 I don't fully understand the reason of this change, although the Debian
change log 
(https://metadata.ftp-master.debian.org/changelogs/main/g/gcc-mingw-w64/gcc-mingw-w64_25.1_changelog)
says

> It is no longer possible to tweak the installation directory for
> different thread models, so the -posix and -win32 packages are no longer
> co-installable.

so it might not even be the Debian maintainers' decision, but in any case
we'll have to live with it.


 Right now it shouldn't create any problems for us because I believe lmi
has always used "-win32" variants of the packages that still remain the
default ones. In principle, I think it would be better to use the "-posix"
variant as only it provides working std::thread and related classes
currently (I don't lose hope that this will change in the future, but so
far this hasn't happened), and the only drawback is that another MinGW DLL
(winpthreads one) would need to be distributed with the application, but as
long as we don't use std::thread anywhere in lmi code, there is no urgency
to change it.

 So this is, again, just to let you know about this change so that you're
not surprised when you run into it (in particular, upgrading MinGW packages
will uninstall all the "-posix" versions of them, unless you uninstall the
"-win32" ones manually first), as it took me some time to understand what
the actual change was.

 Best regards,
VZ

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