[R-SIG-Mac] GTK+ support (or rather lack thereof)

[Simon Urbanek]

We have a fairly complete coverage of packages for R 4.0.0, but one exception is GTK+ (and thus RGtk2 and its dependencies). It seems that GTK+ has been abandoned several years ago, the documented macOS build doesn't work and there are no released binaries. To make things worse, Gnome has been switching from autoconf to custom build systems that are also broken (quite amazing - the build fails with an error in the build system's headers including Python headers...), so the path of building our own release from scratch is also not realistic anymore (we used to build GTK+ for X11 when it was still possible).

Hence this is a call to the R community to see if anyone actually cares. And if so, if there is any known source or path to macOS binaries (script to build it is fine, too). Unlike regular rules, we would allow dynamic linking as we have granted that exception to GTK+ before, but it has to be compatible with the native system. As a last resort, we could also re-use out GTK+ 2.24.17 binaries from Snow Leopard, but those are considerably old, so I'd prefer not to do that. Comments are welcome.

Thanks,
Simon