WIP: ARM Updates, master branch (2019.05.01.)

These are all the tweaks I put in place to make the CMake configuration succeed on my Raspberry Pi. 😛

I had to teach get_host_binary_tag.py how to recognise the CPU in this little box. Though I have to say I'm really not happy with how that script works. I'm not sure that Gaudi is really the project that should have such things hardcoded. There really should be some better way of doing all this. 🤔

With that script modified, I still didn't manage to find "just the right" platform flags for GCC to make the build work, so I decided to just do the blunt thing, and update GaudiBuildFlags.cmake to only set platform flags for x86_64 for now.

Finally I updated some set(...) calls that started printing warnings with CMake 3.14. The calls were always faulty, CMake just didn't warn about them before. (I saw them already in my Mac builds, but didn't follow up on them there.)

Unfortunately with all this the build still didn't succeed. Raspbian comes with GCC 6.3 out of the box. Which is not able to build the HEAD of the master branch anymore. So I'll have to see about installing a newer version of GCC. But since that may take a while, I thought I'd open a merge request already. But it could be kept waiting until I actually succeed with a build. 😉