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CI: Allow different Regex for OSX

Simon Spannagel requested to merge apple_mt19937 into master

Using C++11 distributions such as std::normal_distribution does not guarantee to provide the same output values across platforms when used with the same random number generator as input.

(cf. https://stackoverflow.com/questions/34903356/c11-random-number-distributions-are-not-consistent-across-platforms-what-al and references therein)

This means, our current approach to producing and using random numbers from C++11 distributions is not portable and the calls will yield different outputs on different platforms even though the PRNG engine (we mostly ise the MT19937 Mersenne Twister) itself guarantees reproducible sequences.

This leaves us with two options:

  • We definitely want to provide this in a portable way - then we would need to write our own implementations of distributions or use some ROOT functionality
  • We only care about reproducibility within the same platform - then we simply need to make sure, the tests use the proper regex for each platform

This MR implements the second approach, since I think this should be enough and portability would really only be a corner case. Let me know if you disagree.

Please review and merge.

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