treewide: disable -Werror for llvm 7

Some of these have errors on newest llvm. It’s easiest to just add
-Wno-error in these cases.

pkgs/tools/misc/toybox/default.nix

@@ -54,6 +54,8 @@ stdenv.mkDerivation rec {
   checkInputs = [ which ]; # used for tests with checkFlags = [ "DEBUG=true" ];
   checkTarget = "tests";
 
+  NIX_CFLAGS_COMPILE = "-Wno-error";
+
   meta = with stdenv.lib; {
     description = "Lightweight implementation of some Unix command line utilities";
     homepage = https://landley.net/toybox/;