Warn if the user's NDK is too high or low.

def check_ndk_api(ndk_api, android_api):
    """Warn if the user's NDK is too high or low."""
    if ndk_api > android_api:
        raise BuildInterruptingException(
            'Target NDK API is {}, higher than the target Android API {}.'.format(
                ndk_api, android_api),
            instructions=('The NDK API is a minimum supported API number and must be lower '
                          'than the target Android API'))

    if ndk_api < MIN_NDK_API:
        warning(OLD_NDK_API_MESSAGE)