Top-level builds including manual tests don't work

The recent wave of moves of examples to manual tests is probably to blame.
Configuring (in an out-of-source build tree) with

.../configure -developer-build -no-optimize-debug -ccache \
    -skip qtwebengine -skip qt3d -make benchmarks -make examples -- \
    -Wno-dev --log-level=NOTICE \
    -DQT_BUILD_EXAMPLES_AS_EXTERNAL=OFF \
    -DQT_BUILD_MANUAL_TESTS=ON \
    && cmake --build . --parallel

I (see a fair few warnings, amid the expected output, and then):

-- Configuring done (59.6s)
CMake Error: AUTOMOC for target sender: The "moc" executable ".../qtbase/libexec/moc" does not exist.
CMake Generate step failed.  Build files cannot be regenerated correctly.
CMake Error at .../qtbase/cmake/QtProcessConfigureArgs.cmake:1063 (message):
  CMake exited with code 1.

semlanik and I have pushed a few patches to Gerrit that address things we could initially see, but the problem remains, even with all those patches applied to yesterday's dev of each module.

In particular, note that the AUTOMOC error message gives no hint to which target CMake was trying to do it for; if we can improve that message to at least identify the target, it might make tracking down similar problems in future "a tad" easier.

Let's try to get manual tests building again …