Allow to build with "-stdlib libc++"
This is potentially a way forward enabling building on I4's lab infrastructure. We do not have a GCC/libstdc++ there that has all the headers we currently need (<compare>
ATM, but we have a libc++-11-dev installed (thanks to apt.llvm.org). Maybe this way we can build EMPER in the I4 lab (without docker) again.
Edited by Florian Schmaus