Merge topic 'cxxmodules-cmp0155-graceful-fallback-without-scanner' into release-3.28

1f507580a1 cmGlobalGenerator: give context about module queries
889aa0354a CMP0155: ignore scanning for sources if no scanner is available

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Merge-request: !8925