Non portable use of arch flags

CMP_Core adds SIMD libraries unconditionally and specifies arch/march flags. Those flags are compiler dependent and not platform. The build scripts assumes on Windows msvc is being used but clang becomes more and more common as the compiler of choice and then there is mingw. An other issue is that -march=nehalem and co require an x86 target host to be accepted.

Probably the SIMD libs should be put behind options, ifdefs and the needed flags be fed via presets.