Improve diagnostics for #28

[anton-malakhov]

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@AlexVeprev @tbbdev

[AlexVeprev]

There were a lot of changes, so the proposed implementation doesn't work anymore, but the idea may still be actual. @anton-malakhov, does it still make sense? If so maybe you can create an issue describing use cases where you need it. I'd like to understand if you need the diagnostics improvements for oneDPL configuration or you want to use FindTBB separately somewhere? I'd not recommend the second scenario since the current FindTBB covers oneDPL use cases, but may not be fully reliable as a separate unit for other projects.

[anton-malakhov]

if version is correct and diagnostics are there already - please close, otherwise convert to an issue or feature request to add message and test if the version it reports matches TBB version.