Fix evaluation with old versions of nixpkgs

Using an old version of nixpkgs with ghc.nix fails to evaluate:

error: undefined variable 'happy'
at /nix/store/g8fnx3r5jccwgwhiridj6rlmqwd80cmi-source/ghc.nix:270:20:
   269|     export GHCPKG=$NIX_GHCPKG
   270|     export HAPPY=${happy}/bin/happy
      |                    ^
   271|     export ALEX=${alex}/bin/alex

Using hspkgs.happy instead of happy (which defers to pkgs.happy due to the with pkgs; clause on line 85 fixes this.

added 3 commits

• 3d1a9e93...da25d54b - 2 commits from branch ghc:main
• 32c4126d - Fix with old nixpkgs

Compare with previous version

approved this merge request

thank you

merged

mentioned in commit 7e327d39