Fabian Wein authored Mar 21, 2021 and Florian Toth committed Mar 29, 2021

* CFS_NATIVE has max 20% benefit for Xenon and much less on AMD and Mac
* fix compile errors and warnings for clang-12
* optimization flags are in CFS_OPT_FLAGS
* CFS_OPT_FLAGS is set in compiler.cmake and applied in
  FindCFSDEPS.cmake for CFSDEPS_*_FLAGS
* CFSDEPS_*_FLAGS could deserve some love for C++/C/Fortran differences
* Intel could deserve some love