def METHOD_NAME(compiler):
    """Detects compiler flag to enable C99"""
    gnu_flag = '-std=c99'
    flag_by_cc = {
        'msvc': None,
        'intelw': '/Qstd=c99',
        'intelem': '-std=c99'
    }
    flag = flag_by_cc.get(compiler.compiler_type, gnu_flag)
    if flag is None:
        return None
    if has_flag(compiler, flag, ext='.c'):
        return flag
    from numpy.distutils import log
    log.warn('Could not detect c99 standard flag')
    return None