remove allow-run-as-root in MPIEXEC_PREFLAGS it is handled via the environment variables in the docker images
check for intelclang or clang before checking for OpenMP bug

Michael Kuron authored 4 years ago and Markus Holzer committed 4 years ago

Some optional components use Boost MultiArray and PropertyTree, so we still include the headers if available.
We also still search std::experimental for any, filesystem and optional because some otherwise C++17-compliant compilers did not support them in std until recently.