Fix ghc-lib build failure with 8.10.7 and -haddock

[shayne-fletcher]

ghc-9.2.3 flavored ghc-lib builds fail with ghc-8.10.* when -haddock is enabled due to a particular comment.

• upstream ticket https://gitlab.haskell.org/ghc/ghc/-/issues/20920
• relates to issue Doesn't build on GHC 8.10 when -haddock is enabled #344
• fixes ghc-lib-9.2.3.20220527 doesn't build on GHC 8.10 when -haddock is enabled #391

packages produced via:

stack runhaskell \
  --package extra --package optparse-applicative CI.hs -- \
  --ghc-flavor ghc-9.2.3 

tested with this cabal.project:

packages:    */*.cabal
with-compiler: /Users/shayne/ghc-8.10.7/bin/ghc
package ghc-lib-parser
  ghc-options: -j -haddock   
package ghc-lib
  ghc-options: -haddock

before the fix, cabal new-build all produces:

compiler/GHC/CmmToAsm/AArch64/CodeGen.hs:176:15: error:
    parse error on input ‘{- | debugIsOn -}’
    |
176 | ann doc instr {- | debugIsOn -} = ANN doc instr
    |               ^^^^^^^^^^^^^^^^^

after the fix cabal new-build all runs to completion.

[shayne-fletcher]

cc @garyverhaegen-da @akrmn @sofiafaro-da @cocreature

[akrmn]

thank you!

[akrmn]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[shayne-fletcher]

@akrmn good to land?

[shayne-fletcher]

note: a more direct way to test this configuration: stack runhaskell --resolver lts-18.16 --package extra --package optparse-applicative CI.hs -- --ghc-flavor ghc-9.2.3 --ghc-options "-haddock" --no-checkout --resolver lts-18.16