def METHOD_NAME(compiler):
    """Return the -std=c++[11/14] compiler flag.
    The c++14 is prefered over c++11 (when it is available).
    """
    if has_flag(compiler, "-std=c++14"):
        return "-std=c++14"
    elif has_flag(compiler, "-std=c++11"):
        return "-std=c++11"
    else:
        raise RuntimeError('Unsupported compiler -- at least C++11 support '
                           'is needed!')