libUXGtk.so — UXKit's GTK 4 back end for Linux (x86-64), for xcc 0.7

A Linux GUI program built with UXKit links it with xcc's glibc mode:

    xcc -A x86_64 -dynamic app.xc -L <this directory> -lUXGtk -lgtk-4 [-lGL]

The running machine needs glibc 2.34 or later and GTK 4 (this build is against
GTK 4.22; an older GTK 4 may lack a symbol it uses). Linking from a Mac also
needs a copy of the target's libgtk-4.so (and libGL.so) on the -L path.

UXKit is LGPLv3 (COPYING.LESSER, which builds on COPYING). The library's source
is in src/: libUXGtk.c, with build_libuxgtk.sh, which rebuilds it against the
GTK 4 on any Linux machine.
