The appstream check can already fail due to deprecation warnings and it
is not a good idea having package builds fail due to that. Therefore the
tests are also no longer run by default after recent changes in
c++utilities.
* Remove `mesa` as dependency; `qt5-base` and `qt6-base` both depend on it
and none of the projects depend on it directly; official Qt-based
packages like `qtcreator` also don't depend on `mesa`
* Add `libx11` as dependency of `qtutilities` and variants as it is
actually used directly by those packages for the capslock detection (even
though that feature was broken for quite some time)
* Use an older glibc so resulting binaries can run
on older systems (without having to link statically
against glibc)
* Call packages static-compat-* to make it clear that
these packages are intended for compatibility with
older distributions
* Add further libraries to get static-compat-qt6-base
and some other static-compat-qt6-* packages building
Basically works, tested under the latest Windows 10
TODOs:
* The CLI-only syncthingctl is quite big, maybe some dependencies got
pulled into the build, e.g. through plugins
* Translations are not working because the CMake module providing the
macros is not available in the mingw-w64 build of Qt 6
