Fix compiler flag passing in Python API CMake file

To support cross-compilation of the driver library Swig C wrapper for
the Python API, the CMake file must pass on the C and CXX flags that
have been setup by the build environment so that the correct flags,
include paths etc are used when building the wrapper.

Change-Id: I6288016056c5a4eeef1162ea2a9afb1e3ab4b86a