Fixes #3899

When cabal new-repl spawns ghci, it spawns this as a subprocess.
In UNIX like systems, if a CTRL+C is sent to this child process
it also bubbles up to the parent process, causing it to terminate.
Also see https://hackage.haskell.org/package/process-1.4.2.0/docs/System-Process.html#g:4.

However, this is not what we want for interactive subprocesses.
Interactive processes usually define their own handlers for CTRL+C,
for example GHCi uses CTRL+C to reset the input buffer. So instead
of terminating on CTRL+C we want to delegate CTRL+C to GHCi
and let it do its thing.

Luckily, we can enable CTRL+C delegation such that the parent
process ignores the CTRL+C and instead delegates it to the
child process.