[DUX-3008] The prompt is not necessarily on a newline

[9999years]

Oops:

$ ghci
GHCi, version 9.10.1: https://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /Users/wiggles/.ghci
ghci> putStr "foo"
fooghci>

Ghciwatch thinks this will never happen.

Also, we should remove the hacky fix from https://github.com/MercuryTechnologies/ghciwatch/pull/345 when we fix this.

_{From SyncLinear.com | DUX-3008}