https://github.com/cc65/cc65/commit/b2657ecef5c0db061587c4f98e94b7500c74a93f
Nice find!
It's so very, very cool that someone did that and cooperated with the CC65 team to get it integrated!
...what is it again?
It's a more standards-compliant C compiler that can be used to replace HuC with something a little more modern.
Getting the PCE support mainstreamed into the official CC65 package is a big deal!