System OpenMP used for linking when building, conda OpenMP used when running

[johnlees]

If building locally, in CMake find_package(OpenMP) gets the system OpenMP. But if you use a conda LD_LIBRARY_PATH this will potentially specify a different version at runtime. In many cases they are the same, but llvm-omp may cause segfaults etc

This isn't a problem on the conda build, as conda-forge doesn't have a system openmp and fixes the rpath at the end.

I couldn't work out how to change this by modifying this command in CMake

[johnlees]

This isn't straightforward to fix - see https://github.com/Kitware/CMake/blob/master/Modules/FindOpenMP.cmake
This compiles a test program and looks for the OpenMP flags used. No variables than can be overriden here.

One option would be to remove OpenMP::OpenMP_CXX and add flags from:

• OpenMP_CXX_LIB_NAMES (gomp;pthread)
• OpenMP_CXX_INCLUDE_DIRS
• OpenMP_CXX_FLAGS

[johnlees]

As of #44 this is manually done in CMakeLists