Buliding on arm broke in 7.4.1
As you can see here: https://buildd.debian.org/status/logs.php?pkg=ghc&arch=armel the GHC build fails on armel on Debian, and the change was introduced between the last release candidate and the final release. This is not a good time to make such changes, as it makes testing the release candidates somewhat obsolete. *slightgrumble*
The problematic change was most likely [50c07f74] but I can’t offer any productive advice, sorry.