cmake: Fixes for online standalone build.

These changes allow embedding the online code in other cmake projects as a subproject.

added Build System Externals Online labels

assigned to @fweig

added 2 commits

• 3d41fe4e - 1 commit from branch computing:master
• 7c133790 - cmake: Fixes for online standalone build.

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Dear @d.smith, @fweig, @f.uhlig,

you have been identified as code owner of at least one file which was changed with this merge request.

Please check the changes and approve them or request changes.

added CodeOwners label

added 4 commits

• 7c133790...39c00e70 - 3 commits from branch computing:master
• 7a75bd26 - cmake: Fixes for online standalone build.

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added 3 commits

• 7a75bd26...a12ee31f - 2 commits from branch computing:master
• 04e25bd4 - cmake: Fixes for online standalone build.

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enabled an automatic merge when the pipeline for 04e25bd4 succeeds

merged