treewide: Replace meta.available checks in shouldUsePackages copypasta

This reverts commit 79d8353b5e.

This sort of code breaks config.{allowBroken, allowUnsupportedSystem} =
true by making them do unpredictable things.

pkgs/os-specific/linux/ffado/default.nix

@@ -11,7 +11,7 @@
 
 let
 
-  shouldUsePkg = pkg: if pkg != null && pkg.meta.available then pkg else null;
+  shouldUsePkg = pkg: if pkg != null && stdenv.lib.any (stdenv.lib.meta.platformMatch stdenv.hostPlatform) pkg.meta.platforms then pkg else null;
 
   libOnly = prefix == "lib";