Support macos system to use ghcs-nix

Currently, building ghcs.nix on macos does not work.

 % nix build -f . ghc-9_6_1-alpha2 
error: cannot coerce null to a string

       at /Users/ianwookim/repo/srcc/ghcs-nix/hadrian.nix:151:23:

          150|     # Unicode locale.
          151|     LOCALE_ARCHIVE = "${glibcLocales}/lib/locale/locale-archive";
             |                       ^
          152|     LANG = "C.UTF-8";
(use '--show-trace' to show detailed location information)

Supporting macos will be very benefitable as more developers can easily access multiple versions of GHCs. Thanks!