As per IEEE Std 1003.1-2017, Section 8.3, TERM and
SHELL vars says we are running GIMP on POSIX shell.
They are not set by either the deprecated Windows CMD
nor by Windows PowerShell since they are not POSIX.
POSIX shells are supported by us on Linux and macOS but
actually not on Windows, since they are non-native: they
rely on forking to Cygwin which have terrible performance
(##11385) and do other tricks to make deps believe they
are on Unix which breaks e.g. GObject Introspection (#11424).
Anyway, it is Unix emulation at its prime, tricky by nature.
Even so, does not hurt allow the output on these
unsupported shells on Windows so not disrupt workflows
of adventurous developers but they will be warned that
problems (like the ones above) can and indeed appear.
Previously we were only passing this information on the debug dialog
when debugging warnings and criticals. Now it will also have the
information for crashes, hence recommending people to update their GIMP
instead of reporting bugs on old versions.
Instead of making the focus on bug reporting, the debug dialog will now
make the focus on updating the application if it is found that one is
not using the last version.
Debug data (backtraces and co.) will still be available and copiable,
but under an expander, and bug report button won't be displayed (i.e.
data will still be available upon request but we don't push anymore
people to submit it directly if they are using old versions of GIMP).
Of course, if you are using the last version (or version check was not
possible), the dialog still stays the same.
Move gimp-debug-tools.c from tools/ to a new app-tools/ subdir,
which should contain external tools needed by app/, and which is
built *after* app/ (unlinke tools/). This allows gimp-debug-tool
to depend on libapp and libappwidgets, instead of on actual source
files from app/. Building sources from app/ in another subdir
screws with the distclean rules, and breaks distcheck.
