Merge topic 'cxxmodules-no-unity'

63bbb3768d cmLocalGenerator: ignore scanned sources for unity builds
76b5383123 cmGlobalGenerator: add unity sources after computing target compile features
7fc2a83fe6 Tests/CXXModules: add a test with unity build support

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Merge-request: !9118