CMake/Swig updates for python wrapper

CMake/Swig updates for python wrapper

libftdi was FTBFS[1] in Fedora Rawhide after a GCC 9.0.X mass rebuild but
the problem turned out to be behavior changes[2] in CMake with regards to
SWIG[3].

The UseSWIG module in cmake 3.13+ will now use standard target names and not
generate the SWIG_MODULE_<target>_REAL_NAME variable.

Replace the deprecated swig_add_module with swig_add_library.

[Refinements from Intra2net:
- Use swig_add_library for cmake 3.8+ only
- Add cmake version guard for the new CMP0078 policy
- Use "NOT CMAKE_VERSION VERSION_LESS" construct to
  support cmake versions below 3.7.0]

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1675275
[2] https://cmake.org/cmake/help/latest/policy/CMP0078.html?highlight=cmp0078
[3] https://cmake.org/cmake/help/latest/module/UseSWIG.html