Investigate PyNomad with OpenMP enabled

[ctribes]

In version 4.2 and above, PyNomad building requested to disable OpenMP. Weird crashes was observed. Maybe related to Gil releasing.
Look into Pyx code. Test again on all platforms with version > 4.3.1.

[ctribes]

On version 4.3.1, building and run tests work fine with OpenMP. More tests are required before putting this as a default for next release.

To enable OpenMP (if available), the root CMakeLists.txt needs to be modified (see below the commented lines).

#
# Choose to build the Python interface
#
option(BUILD_INTERFACE_PYTHON "Option to build Python interface to Nomad" OFF)
if(BUILD_INTERFACE_PYTHON MATCHES ON)
#   if(OpenMP_FOUND)
#       message(STATUS "  Warning: Cannot build Python interface with OpenMP enabled")
#   else()
       find_package(Python 3.6 QUIET REQUIRED)
       message(CHECK_START "  Configuring build for Python interface")
       add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/interfaces/PyNomad)
       message(CHECK_PASS " done")
#   endif()
else()
   message(STATUS "  Python interface to Nomad NOT built")
endif()

The build directory AND $NOMAD_HOME/interfaces/PyNomad/[build,PyNomad.....so] need to be removed.

Run the config command again and build.

cmake -DBUILD_INTERFACE_PYTHON=ON -S . -B build/release