It's also worth appreciating that in the case of the xz project, the CMake flow is secondary other than for Windows. While I have no evidence one way or another, I wonder if the period in the CMake test that disabled Linux Landlock was actually intentional. Since it disabled it for the CMake build and not the autotools build, it seems like it could have been accidental, unless some significant liblzma consumer builds with CMake and would have otherwise had Landlock enabled.
It's also worth appreciating that in the case of the xz project, the CMake flow is secondary other than for Windows. While I have no evidence one way or another, I wonder if the period in the CMake test that disabled Linux Landlock was actually intentional. Since it disabled it for the CMake build and not the autotools build, it seems like it could have been accidental, unless some significant liblzma consumer builds with CMake and would have otherwise had Landlock enabled.