My very last commit to D4904 removed -fobject-code. I should have tested this
more thoroughly, because it is required to do a fresh ghci load, as some code
uses unboxed tuples.
One of my motivations for doing this was that if you run the script without
passing -odir / -hidir, it would pollute the source tree with .hi and .o files.
This also appeared to break subsequent builds. I've made it much less likely
that this will happen by instead specifying -odir and -hidir within the ghci
script rather than on the commandline.
I plan to open a separate diff which adds a test that these scripts work.
Until this patch is merged, the workaround is to do `./utils/ghc-in-ghci/run.sh -fobject-code`