[bug#62056] Custom progress reporter for scripts/substitute.scm

[Richard Sent]

I started investigating this issue for the substitutes script
specifically and it's more challenging than a straightforward isatty?
call. I opened an issue for that here:
https://issues.guix.gnu.org/71299

I agree that modifying erase-current-line isn't the right solution. I
think it's the responsibility of the caller to ensure that the output
port is appropriate.

-- 
Take it easy,
Richard Sent
Making my computer weirder one commit at a time.