meson: Fix install mode of Xorg SUID wrapper

Merged Povilas Kanapickas requested to merge p12tic/xserver:meson-suid-wrapper-mode into master

Meson 0.47.0 is newer than our currently required version 0.46 by just several months, so we can start depending on it and fix install_mode for the Xorg SUID wrapper.

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