[cmake] Remove error in Findcxxopt

[bakpaul]

Remove error and send warning when cxxopt is found but version mismatch

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• it builds with SUCCESS for all platforms on the CI.
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[olivier-roussel]

I guess you want to avoid critical error on cmake and rather it continue by fetching cxxopts in case of version mismatch ?

[bakpaul]

Esatto ! Avoid having to uninstall the package...

[olivier-roussel]

Indeed sounds good !