macOS compatibility

[ruberith]

These adaptations allow builds using Clang on recent versions of macOS (tested on Apple silicon):

• Recent versions of CMake automatically determine the correct flags for OpenMP and provide a target to link against. Nevertheless, Clang does not include an OpenMP implementation on macOS by default, but the user can easily install a build of LLVM libomp (e.g. via Homebrew) to be shared by all projects requiring OpenMP which is then detected by CMake.
• Clang is also missing an implementation of the Parallel STL algorithms, so I suggest to add oneDPL as a dependency. oneDPL provides the same interface as the standard library to TBB (which is used by GCC) among others and can be installed by the user in a similar fashion to libomp.