darcs: Fix build (Use old GHC)

This is fixed at upstream's head; this change can be reverted after
darcs cuts a new release (current release is 2.14.2).

pkgs/development/haskell-modules/configuration-common.nix

@@ -1498,4 +1498,8 @@ self: super: {
     # version of Polysemy the plugin goes with
     polysemy = self.polysemy_1_3_0_0;
   };
+
+  # Fixed at head, but hasn't cut a release in awhile.
+  darcs = doJailbreak super.darcs;
+
 } // import ./configuration-tensorflow.nix {inherit pkgs haskellLib;} self super

pkgs/development/haskell-modules/configuration-hackage2nix.yaml

@@ -3953,7 +3953,6 @@ broken-packages:
   - Dao
   - dao
   - dapi
-  - darcs
   - darcs-benchmark
   - darcs-beta
   - darcs-buildpackage

pkgs/top-level/all-packages.nix

@@ -18883,7 +18883,7 @@ in
 
   dablin = callPackage ../applications/radio/dablin { };
 
-  darcs = haskell.lib.overrideCabal (haskell.lib.justStaticExecutables haskellPackages.darcs) (drv: {
+  darcs = haskell.lib.overrideCabal (haskell.lib.justStaticExecutables haskell.packages.ghc865.darcs) (drv: {
     configureFlags = (stdenv.lib.remove "-flibrary" drv.configureFlags or []) ++ ["-f-library"];
   });