The configuration tests for wayland-client and wayland-egl were deleted in https://codereview.qt-project.org/c/qt/qtwayland/+/274421 . Unfortunately, some tests were not converted to inline format, but were still deleted. So they will now fail because they can't be found.
Unfortunately, the way configuration works, is that it will happily build nothing if the configure tests for libwayland fails (no errors, green coin builds).
In short: qtwayland client and compositor modules are not currently built, nor tested in the 5.15 and dev branches.