Otherwise vectorization will fail

This reverts merge request !370

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.

Markus Holzer authored 4 years ago and Dominik Thoennes committed 4 years ago

also clean up some old leftovers nearby

The default target of \file is the current file.

- checking order of integrator
- checking energy conservation
- added semi implicit euler
- improved documentation
- playground for integrator analysis

The test initialy contained two tests. To reduce runtime,
the two tests were separated.

Since MSVC only has beta support for OpenMP 2.0 firstprivate
cannot be used for these compilers. However, firstprivate
is necessary for a reasonably safe implementation of OpenMP
in MESA-PD. The solution is to move OpenMP support to the
generator and disable OpenMP for the checked in version.
The waLBerla OpenMP guards are removed as they are no longer
needed. It is now assumed that if MESA-PD is generated with
OpenMP support it is about to be used. If OpenMP is disabled
with CMake warnings will pop up about undefined pragmas.