Merge topic 'cxxmodules-clang-update'

5dc17d0a7a gitlab-ci: update to new Clang CI image for C++ modules
e84fcbcb0b cxxmodules: support new round of Clang patches
5e35913382 ci: update `llvm` snapshot to newest patch revisions

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Merge-request: !8019