WTFGType is using volatile improperly when defining the get_type() macro, because the code is copied from GLib, which had the same bug. See: https://gitlab.gnome.org/GNOME/glib/-/issues/600#note_877282
Created attachment 414813 [details] Patch
Honestly I'm not sure why this is a hard build failure. It causes a -Wincompatible-pointer-types warning. Maybe the compiler people decided to test a build with -Werror=incompatible-pointer-types enabled? Regardless, it's nice to see such problems pop up early, rather than waiting until after GCC 11 hits Fedora next year....
Committed r270166: <https://trac.webkit.org/changeset/270166> All reviewed patches have been landed. Closing bug and clearing flags on attachment 414813 [details].