Since version 9.4.7-1, ghc fails to build on the GNU/Hurd port of Debian,
see

https://buildd.debian.org/status/fetch.php?pkg=ghc&arch=hurd-i386&ver=9.4.7-1&stamp=1697717885&raw=0

Error, rule finished running but did not produce file:
  _build/stage0/lib/i386-gnu-ghc-9.4.6/ghc-boot-th-9.4.7/libHSghc-boot-th-9.4.7.a

and indeed, what did get produce was rather
_build/stage0/lib/i386-hurd-ghc-9.4.6/ghc-boot-th-9.4.7/libHSghc-boot-th-9.4.7.a
(i386-hurd instead of i386-gnu).

This is due to confusion between hurd and gnu in various places.  Apparently
previous versions of ghc were using gnu for the GNU/Hurd port, and thus
putting libraries etc. in i386-gnu. So we have to follow the existing
practice.