BNFC tarball ships `Lex.hs` and `Par.hs`

This affects all releases of BNFC 2.9 and most of 2.8.
Not affected: 2.8.1, 2.8.3.1

It is not clear though whether this makes cabal skip the alex and happy steps. So it could be a cosmetic issue. I had some problem with 2.8.3 (fixed in 2.8.3.1), but that shipped several copies of Lex.hs:

BNFC-2.8.3/dist/build/unit-tests/unit-tests-tmp/LexBNF.hs
BNFC-2.8.3/dist/build/bnfc/bnfc-tmp/LexBNF.hs
BNFC-2.8.3/src/LexBNF.hs

https://github.com/haskell/cabal/issues/7808
https://github.com/haskell/cabal/issues/7258

Today I witnessed a build failure of BNFC with an old alex (using GHC 9.4 with alex 3.2.5). Maybe this can be fixed by requiring a new alex and happy in the build-tool-depends section that create output valid for all GHCs we support (8 and 9 so far). Reproducer would be:

install alex-3.2.5
install recent GHC, e.g. 9.4.7
cabal install BNFC-2.9.5

BNFC / bnfc

BNFC tarball ships `Lex.hs` and `Par.hs` #467