Meson: Make documentation optional and override wayland-scanner program
commit b1396809 Meson: Override wayland-scanner program
In the case wayland is used as a subproject, this will cause any other
projects to use wayland_scanner_for_build value when they do
find_program('wayland-scanner').
commit 7c0ba853 Meson: Make building documentation optional by default
This uses a "feature" option that can have enabled/disabled/auto values.
In the case of auto we just skip build the documentation if one of the
tools are missing.
This requires Meson >=0.60.0 to be able to keep true/false values
working but as deprecated.
Edited by Xavier Claessens