build: Enable using default XKB root from recent xkeyboard-config The *default* XKB root directory is now set from the *most recent* xkeyboard-config installed package, in case [multiple versions] are installed in parallel. It also try to use the package-specific XKB root (if available) rather than the X11 root, respectively defined by the pkg-config variables `xkb_root` (xkeyboard-config ≥ 2.45) and `xkb_base`. If no such package is found, it fallbacks to the historical X11 directory, as previously. [multiple versions]: https://xkeyboard-config.freedesktop.org/doc/versioning/