bug#37366: ghci can't find System.IO

[Royce Strange]

Hello.

Found the ghc reported to have issues:
https://ci.guix.gnu.org/build/1567747/details

Going back in time to the commit that corresponds
with the ghc that was reported to be broken:
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$ guix time-machine --commit=caa366ec230ccc42f5c8d90d36e8cac933053a81 \
-- environment --pure --ad-hoc ghc

[env]$ ghci
GHCi, version 8.6.5: http://www.haskell.org/ghc/  :? for help

<interactive>:1:6: error:
    Not in scope: `System.IO.hSetBuffering'
    No module named `System.IO' is imported.

<interactive>:1:30: error:
    Not in scope: `System.IO.stdin'
    No module named `System.IO' is imported.
...
...
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It was indeed broken.

I believe 83aa6562173e06e8fafd4857a2e708feabfe56f8 fixed this.
Validating that ghci can actually start properly now
with a current version of guix:
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$ guix --version
guix (GNU Guix) 2971ed57345ee4e00058efeaf27c6a0790fdc9dd

$ guix environment --pure --ad-hoc ghc -- ghci
GHCi, version 8.6.5: http://www.haskell.org/ghc/  :? for help
Prelude> 1 + 2
3
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Going to go ahead and close.