treewide: mark packages as buildable on darwin (PR #45364)

vcunat amended the commit a bit; see the PR for details/discussion.

pkgs/development/libraries/iml/default.nix

@@ -23,7 +23,7 @@ stdenv.mkDerivation rec {
     description = ''Algorithms for computing exact solutions to dense systems of linear equations over the integers'';
     license = stdenv.lib.licenses.gpl2Plus;
     maintainers = [stdenv.lib.maintainers.raskin];
-    platforms = stdenv.lib.platforms.linux;
+    platforms = stdenv.lib.platforms.unix;
     homepage = https://cs.uwaterloo.ca/~astorjoh/iml.html;
     updateWalker = true;
   };