Improved architecture detection and compatiblity check

the reported architecture now matches the architecture name from https://gcc.gnu.org/onlinedocs/gcc-8.2.0/gcc/x86-Options.html#x86-Options, so we get haswell-centos7 instead of x86_64+avx2+fma-centos7 (or x86_64-centos7,avx2+fma).

The interface still understands old style platforms, but internally it maps them to the new convention.

Closes LBCORE-1696