This prevents possible deadlocks during reduction at the cost of an
additional communication.

the wrapper did not compile but since this was not a problem in the last two years it can be removed

constructing an empty std::set has almost no cost

- OpenMP pragma parser bug
- std::string doesn’t like to be aligned to more than 256 bits

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.