Add "generate_python_ast_h" and "generate_python_ast_c" targets
Add "generate_python_ast_h" and "generate_python_ast_c" targets

jcfr/python-cmake-buildsystem,davidsansome/python-cmake-buildsystem,thewtex/python-cmake-buildsystem,thewtex/python-cmake-buildsystem,python-cmake-buildsystem/python-cmake-buildsystem,adrianbroher/python-cmake-buildsystem