If the flag enableIntegerSimple is true GHC will be build with the GPL-free but
slower integer-simple library instead of the faster but GPLed integer-gmp
library.
The attribute `pkgs.haskell.compiler.integer-simple."${ghcVersion}"` provides a
GHC compiler build with `integer-simple`.
Similarly, the attribute `pkgs.haskell.packages.integer-simple."${ghcVersion}"`
provides a package set supporting `integer-simple`.
Closes https://github.com/NixOS/nixpkgs/pull/22121.
Closes https://github.com/NixOS/nixpkgs/issues/5493.
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.
