The $lib output refers to the terminfo database in $out, which is about
10x larger than the ncurses shared library. Splitting these outputs
saves a small amount of space for any derivations that use the terminfo
database but not the ncurses library, but we do not have evidence that
any such exist.
The new GHC version contains a patch [1] that passes linker and compiler flags
to GCC via response files rather than directly on the command-line. This is
supposed to be beneficial on Windows and other platforms that have trouble
dealing with long argument lists. On NixOS, however, this feature breaks the
flag handling provided by gcc-wrapper [2] and therefore causes the entire GHC
build to fail.
This issue has been reported upstream at [3]. It's not clear yet how to remedy
this problem, but until we've figured that out we just don't pass compiler flags
in response files on NixOS to fix https://github.com/NixOS/nixpkgs/issues/10752.
[1] 296bc70b5f
[2] https://github.com/NixOS/nixpkgs/issues/11762
[3] https://ghc.haskell.org/trac/ghc/ticket/11147
