Merge 'staging' into closure-size

- there were many easy merge conflicts
- cc-wrapper needed nontrivial changes

Many other problems might've been created by interaction of the branches,
but stdenv and a few other packages build fine now.

pkgs/tools/misc/findutils/default.nix

@@ -40,6 +40,8 @@ stdenv.mkDerivation rec {
           * xargs - build and execute command lines from standard input.
     '';
 
+    platforms = stdenv.lib.platforms.all;
+
     license = stdenv.lib.licenses.gpl3Plus;
   };
 }