:return: ccache directory for the current platform

def default_ccache_dir() -> str:
    """:return: ccache directory for the current platform"""
    # Share ccache across containers
    if 'CCACHE_DIR' in os.environ:
        ccache_dir = os.path.realpath(os.environ['CCACHE_DIR'])
        try:
            os.makedirs(ccache_dir, exist_ok=True)
            return ccache_dir
        except PermissionError:
            logging.info('Unable to make dirs at %s, falling back to local temp dir', ccache_dir)
    # In osx tmpdir is not mountable by default
    import platform
    if platform.system() == 'Darwin':
        ccache_dir = "/tmp/_mxnet_ccache"
        os.makedirs(ccache_dir, exist_ok=True)
        return ccache_dir
    return os.path.join(os.path.expanduser("~"), ".ccache")