Choosing a different nodejs for armv5tel.

nodejs 0.12 doesn't build in armv5 or without fpu, it seems.
I tested this change on armv5tel, branch staging.

pkgs/development/web/nodejs/default.nix

@@ -2,6 +2,10 @@
 , pkgconfig, runCommand, which, unstableVersion ? false
 }:
 
+# nodejs 0.12 can't be built on armv5tel. Armv6 with FPU, minimum I think.
+# Related post: http://zo0ok.com/techfindings/archives/1820
+assert stdenv.system != "armv5tel-linux";
+
 let
   dtrace = runCommand "dtrace-native" {} ''
     mkdir -p $out/bin