ghcjs: properly wrap binaries in environment

This also:

 1  Builds Setup.hs with ghcjs, which (among other things) defines
    __GHCJS__ and ghcjs_HOST_OS during pre-processing.
 2  Fixes ghc-paths to point at ghcjs and use NIX_GHCJS_* env-vars.
 3  Boots ghcjs into $prefix/lib/$compiler.

pkgs/development/compilers/ghcjs/default.nix

@@ -39,10 +39,6 @@
 }:
 let
   version = "0.1.0";
-  ghcArch = if pkgs.stdenv.system == "i686-linux"
-    then "i386-linux"
-    else pkgs.stdenv.system;
-  libDir = "share/ghcjs/${ghcArch}-${version}-${ghc.version}/ghcjs";
   ghcjsBoot = fetchgit {
     url = git://github.com/ghcjs/ghcjs-boot.git;
     rev = "ab8765edcb507b8b810e3c324fd5bd5af2b69d8f"; # 7.10 branch
@@ -84,14 +80,19 @@ in mkDerivation (rec {
   ];
   patches = [ ./ghcjs.patch ];
   postPatch = ''
-    substituteInPlace Setup.hs --replace "/usr/bin/env" "${coreutils}/bin/env"
-    substituteInPlace src/Compiler/Info.hs --replace "@PREFIX@" "$out"
+    substituteInPlace Setup.hs \
+      --replace "/usr/bin/env" "${coreutils}/bin/env"
+
+    substituteInPlace src/Compiler/Info.hs \
+      --replace "@PREFIX@" "$out"          \
+      --replace "@VERSION@" "${version}"
+
     substituteInPlace src-bin/Boot.hs \
       --replace "@PREFIX@" "$out"     \
       --replace "@CC@"     "${stdenv.cc}/bin/cc"
   '';
   preBuild = ''
-    local topDir=$out/${libDir}
+    local topDir=$out/lib/ghcjs-${version}
     mkdir -p $topDir
 
     cp -r ${ghcjsBoot} $topDir/ghcjs-boot
@@ -116,9 +117,9 @@ in mkDerivation (rec {
         --with-gmp-libraries ${gmp}/lib
   '';
   passthru = {
-    inherit libDir;
     isGhcjs = true;
     nativeGhc = ghc;
+    inherit nodejs;
   };
 
   homepage = "https://github.com/ghcjs/ghcjs";

pkgs/development/compilers/ghcjs/ghcjs.patch

@@ -60,15 +60,21 @@ index 3c68dcf..64f3cf7 100644
             , "--haddock-html"
  -- workaround for hoogle support being broken in haddock for GHC 7.10RC1
 diff --git a/src/Compiler/Info.hs b/src/Compiler/Info.hs
-index 33a401f..5d09c86 100644
+index 33a401f..79833c5 100644
 --- a/src/Compiler/Info.hs
 +++ b/src/Compiler/Info.hs
-@@ -49,7 +49,7 @@ compilerInfo nativeToo dflags = do
+@@ -48,13 +48,7 @@ compilerInfo nativeToo dflags = do
+
  -- | the directory to use if started without -B flag
  getDefaultTopDir :: IO FilePath
- getDefaultTopDir = do
+-getDefaultTopDir = do
 -  appdir <- getAppUserDataDirectory "ghcjs"
-+  let appdir = "@PREFIX@/share/ghcjs"
-   return (appdir </> subdir </> "ghcjs")
-       where
-         targetARCH = arch
+-  return (appdir </> subdir </> "ghcjs")
+-      where
+-        targetARCH = arch
+-        targetOS   = os
+-        subdir     = targetARCH ++ '-':targetOS ++ '-':getFullCompilerVersion
++getDefaultTopDir = return "@PREFIX@/lib/ghcjs-@VERSION@"
+
+ getDefaultLibDir :: IO FilePath
+ getDefaultLibDir = getDefaultTopDir