Update CI config to clang-7

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mentioned in merge request !14 (merged)

added 3 commits

• 867df3c9...26f4a513 - 2 commits from branch master
• f72e7f99 - Update CI config to clang-7

Compare with previous version

enabled an automatic merge when the pipeline for f72e7f99 succeeds

merged

mentioned in commit 2103a363