ERROR: LAPACK library not found - have that installed or set BOB_PREFIX_PATH to point to the correct installation prefix

See: https://gitlab.idiap.ch/bob/bob.math/-/jobs/116298

As far as I have investigated this so far, there are two problems here:

1. numpy compile flags (mkl_rt and pthread) are being ignored because bob.extension.utils.findlibrary cannot find pthread which is located in /x86_64-conda_cos6-linux-gnu/sysroot/usr/lib during build.
2. As an alternative we search for mkl_lapack64 which is not available in MKL 2017 and MKL 2018. I don't when was this available in MKL that we are searching for it.

@andre.anjos ideas on 1? @tiago.pereira ideas on 2? Why are we not searching for mkl_rt instead? It seems to be available in both mkl 2017 and 2018.