Our packages from the GTK/GLib world in our build environment are rather old. Besides wanting new features and bug fixes, this also makes them block the upgrade of gcc (bug 8361). Note that we only have GTK for Dia, which means it is GTK2. So the focus is more on the other related packages.
Newer GLib and friends ideally need newer MinGW and newer macOS SDK. Fortunately, we can patch around it and get almost to the latest version. As a side effect of this exploration, PCRE got upgraded as GLib used to require that. But even newer GLib switched to PCRE2 instead. I'm keeping the PCRE upgrade, though, as the work is already done and we use it in other components.