Charlie Marsh
556080225d
Per https://apenwarr.ca/log/20181113, `ctime` should be a lot more conservative, and should detect things like the issue we see with the python-build-standalone builds, where the `mtime` is identical across builds. On Windows, I'm just using `last_write_time`. But we should probably add `volume_serial_number` and other attributes via [`winapi_util`](https://docs.rs/winapi-util/latest/winapi_util/index.html).