Make ASCII external format builtin?

Describe the feature

We currently have :iso-8859-1 and :utf-8 external formats built into the core. Should we include :ascii too?

Is there a prototype?

There's no prototype, but it's not hard to add :ascii external format to the core, just like what we did to make :utf-8 in-core.

Describe the feature in more detail

I noticed this just recently when running configure for maxima when building with cmucl 21e. There are messages that the :ascii format is getting loaded. I don't remember seeing this before, but I was building with snapshot-2021-07 until the recent release of 21e.

I don't know why it's starting to do this now. I also don't know what configure is doing to trigger this.

Not a big deal one way or another.