vmmonad: add backwards-compatible MonadFail compliance

The `fail` method on `Monad` has been removed in `ghc` 8.8+, I added a
conditional compilation statement according to what was indicated in the
following wiki article:
<https://gitlab.haskell.org/ghc/ghc/wikis/proposal/monad-fail#adapting-old-code>

* src/VMMonad.hs: Here.
1 job for bb/fix-fail-monad in 46 seconds (queued for 1 minute and 36 seconds)
Status Job ID Name Coverage
  Test
failed #82315
debian-stable-gcc

00:00:46

 
Name Stage Failure
failed
debian-stable-gcc Test
[19 of 35] Compiling VMMonad          ( src/VMMonad.hs, src/VMMonad.o )

src/VMMonad.hs:70:3: error: parse error on input `fail'
|
70 | fail = Fail.fail
| ^^^^
make: *** [Makefile:1423: src/havm] Error 1
make: Target 'all' not remade because of errors.
ERROR: Job failed: exit code 1