Fix elm-reactor.

The elm-reactor setup.hs file tries to build an elm file that's not
distributed in the cabal archive. The archive contains the
already-compiled js file so the step is unnecessary and I'm patching
it out.

pkgs/development/compilers/elm/0001-remove-custom-build-step.patch

@@ -0,0 +1,25 @@
+From a164f7a2b662831ba26f5cebce23f97f1b5afccd Mon Sep 17 00:00:00 2001
+From: Tom Hunger <tehunger@gmail.com>
+Date: Thu, 8 Jan 2015 14:07:17 +0000
+Subject: [PATCH] remove-custom-build-step
+
+---
+ Setup.hs | 2 --
+ 1 file changed, 2 deletions(-)
+
+diff --git a/Setup.hs b/Setup.hs
+index 6f80fd8..a45ffc1 100644
+--- a/Setup.hs
++++ b/Setup.hs
+@@ -19,8 +19,6 @@ main =
+ myPostBuild :: Args -> BuildFlags -> PackageDescription -> LocalBuildInfo -> IO ()
+ myPostBuild args flags pd lbi =
+   do  putStrLn "Custom build step: compiling debuggerInterface.elm"
+-      buildInterface
+-      concatJS lbi
+       postBuild simpleUserHooks args flags pd lbi
+ 
+ 
+-- 
+1.9.4
+

pkgs/development/compilers/elm/elm-reactor.nix

@@ -1,5 +1,3 @@
-# This file was auto-generated by cabal2nix. Please do NOT edit manually!
-
 { cabal, blazeHtml, blazeMarkup, cmdargs, elmCompiler, elmMake, filepath
 , fsnotify, HTTP, mtl, snapCore, snapServer, systemFilepath, text
 , time, transformers, unorderedContainers, websockets
@@ -12,6 +10,7 @@ cabal.mkDerivation (self: {
   sha256 = "1qnrxr3wayhw92w6lghchz8avxbxg00w7p6d1vs7mq9q56876jgj";
   isLibrary = false;
   isExecutable = true;
+  patches = [ ./0001-remove-custom-build-step.patch ];
   buildDepends = [
     blazeHtml blazeMarkup cmdargs elmCompiler filepath fsnotify HTTP
     mtl snapCore snapServer systemFilepath text time transformers
@@ -22,6 +21,6 @@ cabal.mkDerivation (self: {
     description = "Interactive development tool for Elm programs";
     license = self.stdenv.lib.licenses.bsd3;
     platforms = self.ghc.meta.platforms;
-    broken = true;
+#    broken = true;
   };
 })