enabled and mitigated debug warnings in cfg tests

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The suppressed warnings are a mix of

• missing library entries (I only added the ones which actually had documented values - i.e. I did not peak at any headers)
• some known issues
  https://trac.cppcheck.net/ticket/8953
  https://trac.cppcheck.net/ticket/10045
• some so far untracked issues
  (need to reduce and file tickets)

I also encountered the lack of valueFlowBailoutIncompleteVar while investigating one case - see https://trac.cppcheck.net/ticket/12319.

I am not sure if ValueFlow is actually necessary to catch all of these so we could possibly disable it - but that might ahppen implicitly if I ever got around to finish up #4521.