ghc prebuilt: Simplify and harden Darwin fixup

 - Patch all executables and libraries, while skipping scripts. Base at
   least uses libiconv, so should need this too---I suspect it wasn't a
   problem before as we got away with the immpurity.

 - Rather than hardcoding the symlinks to add, do one per mach-o as
   needed

TEMP no -L no script