Fix clang cindex import in macos
In Mac OS, the llvm site-packages path is not automatically added to the python path. Therefore, this MR adds the python path manually to:
PYTHONPATH=$ENV{PYTHONPATH}:${LIBCLANG_LIBDIR}/python${Python_VERSION_MAJOR}.${Python_VERSION_MINOR}/site-packages
This does not affect any other build system.
Edited by Daniel Hugo Campora Perez