haskell infra: nativeGhc != ghc.bootPkgs.ghc

There's no reason to wait for non-binary native to *build* cross ghc,
but we want a nix-built GHC for Setup.hs or things won't work.

pkgs/development/haskell-modules/generic-builder.nix

@@ -1,4 +1,4 @@
-{ stdenv, buildPackages, ghc
+{ stdenv, buildPackages, buildHaskellPackages, ghc
 , jailbreak-cabal, hscolour, cpphs, nodejs
 , buildPlatform, hostPlatform
 }:
@@ -81,7 +81,11 @@ let
                   then "package-db"
                   else "package-conf";
 
-  nativeGhc = if isCross || isGhcjs then ghc.bootPkgs.ghc else ghc;
+  # GHC used for building Setup.hs
+  #
+  # Same as our GHC, unless we're cross, in which case it is native GHC with the
+  # same version, or ghcjs, in which case its the ghc used to build ghcjs.
+  nativeGhc = buildHaskellPackages.ghc;
   nativePackageDbFlag = if versionOlder "7.6" nativeGhc.version
                         then "package-db"
                         else "package-conf";
@@ -147,8 +151,7 @@ let
   ] ++ crossCabalFlags);
 
   setupCompileFlags = [
-    (optionalString (!coreSetup) "-${packageDbFlag}=$packageConfDir")
-    (optionalString isGhcjs "-build-runner")
+    (optionalString (!coreSetup) "-${nativePackageDbFlag}=$packageConfDir")
     (optionalString (isGhcjs || isHaLVM || versionOlder "7.8" ghc.version) "-j$NIX_BUILD_CORES")
     # https://github.com/haskell/cabal/issues/2398
     (optionalString (versionOlder "7.10" ghc.version && !isHaLVM) "-threaded")
@@ -160,14 +163,12 @@ let
   allPkgconfigDepends = pkgconfigDepends ++ libraryPkgconfigDepends ++ executablePkgconfigDepends ++
                         optionals doCheck testPkgconfigDepends ++ optionals doBenchmark benchmarkPkgconfigDepends;
 
-  nativeBuildInputs = [ ghc removeReferencesTo ] ++ optional (allPkgconfigDepends != []) pkgconfig ++
+  nativeBuildInputs = [ ghc nativeGhc removeReferencesTo ] ++ optional (allPkgconfigDepends != []) pkgconfig ++
                       buildTools ++ libraryToolDepends ++ executableToolDepends;
   propagatedBuildInputs = buildDepends ++ libraryHaskellDepends ++ executableHaskellDepends;
   otherBuildInputs = setupHaskellDepends ++ extraLibraries ++ librarySystemDepends ++ executableSystemDepends ++
                      optionals (allPkgconfigDepends != []) allPkgconfigDepends ++
                      optionals doCheck (testDepends ++ testHaskellDepends ++ testSystemDepends ++ testToolDepends) ++
-                     # ghcjs's hsc2hs calls out to the native hsc2hs
-                     optional isGhcjs nativeGhc ++
                      optionals doBenchmark (benchmarkDepends ++ benchmarkHaskellDepends ++ benchmarkSystemDepends ++ benchmarkToolDepends);
   allBuildInputs = propagatedBuildInputs ++ otherBuildInputs;
 
@@ -176,12 +177,14 @@ let
 
   ghcEnv = ghc.withPackages (p: haskellBuildInputs);
 
-  setupBuilder = if isCross then "${nativeGhc}/bin/ghc" else ghcCommand;
   setupCommand = "./Setup";
+
   ghcCommand' = if isGhcjs then "ghcjs" else "ghc";
   ghcCommand = "${ghc.targetPrefix}${ghcCommand'}";
   ghcCommandCaps= toUpper ghcCommand';
 
+  nativeGhcCommand = "${nativeGhc.targetPrefix}ghc";
+
 in
 
 assert allPkgconfigDepends != [] -> pkgconfig != null;
@@ -270,7 +273,7 @@ stdenv.mkDerivation ({
     done
 
     echo setupCompileFlags: $setupCompileFlags
-    ${setupBuilder} $setupCompileFlags --make -o Setup -odir $TMPDIR -hidir $TMPDIR $i
+    ${nativeGhcCommand} $setupCompileFlags --make -o Setup -odir $TMPDIR -hidir $TMPDIR $i
 
     runHook postCompileBuildDriver
   '';