* 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