You may use the --evdev-headers option to the build_ext setuptools command to specify the location of input.h and input-event-codes.h (optionally). It accepts one or more colon-separated paths. For example:

$ python setup.py build_ext \
    --evdev-headers buildroot/input.h:buildroot/input-event-codes.h \
    --include-dirs  buildroot/ \
    install  # or any other command (e.g. develop, bdist, bdist_wheel)

If nothing is specified, build_ext will search in /usr/include/linux by default.