Intel MKL Update, master branch (2022.02.07.)

Updated to taking the Intel MKL libraries from their installer. This way the ATLAS builds would not require having access to /cvmfs/projects.cern.ch/, which is not easily accessible from outside of the CERN firewall.

As before, only the core mathematical libraries are copied into the ATLAS release, leaving most of the MKL installation behind in the build directory.

Since it was so very easy to do, I revived the support for 32-bit builds with MKL. Even if it will likely never be used.

While writing the code, I realised that ExternalProject_Add has supported multiple URLs for the downloads since CMake 3.7. So I decided to specify not just our own location for the installer, but the central Intel one as well. This was of course triggered by the infrastructure issues hitting our latest nightlies. (@fwinkl, we should think of doing this for all of the other packages/externals as well.)

@amete, please have a look. The environment setup was not changed at all, athena.py should find the library in the same way as it did so far.

Finally: Yes, I also find it very unfortunate that we would download an 800 MB file, unpack 8 GBs of files, just to include 40 MBs of libraries in our project. But this still seems like the most robust way of getting these libraries into our releases. @aundrus, you should be aware that the AthenaExternals, AthSimulationExternals, etc. build directories will grow by ~8 GB with this included. Hopefully we will not hit any limits because of this... (For the CI nodes this will be 3x8 GB I think.)