hadrian: Target binary-dist-dir linearises stage1:exe:ghc and stage1:exe:ghc-pkg

The binary-dist-dir target somehow decides to build stage1:exe:ghc-bin completely before stage1:exe:ghc-pkg which is a huge pessimisation because they don't depend on each other at all.

The issue is probably that we first need stage1:exe:ghc-bin and then need stage1:exe:ghc-pkg slightly later but finding out why this happens is pretty tricky.