Adds ghcjs and Asterius as cross compilers (#106)

This adds ghcjs and asterius cross compiler support to haskell.nix.  For proper ghcjs/asterius cross compiler you'll need to add them to nixpkgs.

Author: hamishmack

builder/comp-builder.nix

@@ -157,13 +157,14 @@ let
       "--with-ghc=${ghc.targetPrefix}ghc"
       "--with-ghc-pkg=${ghc.targetPrefix}ghc-pkg"
       "--with-hsc2hs=${ghc.targetPrefix}hsc2hs"
-      # CC
+    ] ++ lib.optionals (stdenv.cc != null)
+    [ # CC
       "--with-gcc=${stdenv.cc.targetPrefix}cc"
       # BINTOOLS
       "--with-ld=${stdenv.cc.bintools.targetPrefix}ld"
       "--with-ar=${stdenv.cc.bintools.targetPrefix}ar"
       "--with-strip=${stdenv.cc.bintools.targetPrefix}strip"
-      # other flags
+    ] ++ [ # other flags
       (if dontStrip then "--disable-executable-stripping" else "--enable-executable-stripping")
       (if dontStrip then "--disable-library-stripping"    else "--enable-library-stripping")
     ] ++ lib.optional doHaddock' "--docdir=${docdir "$doc"}"

lib/host-map.nix

@@ -1,13 +1,24 @@
-stdenv: with stdenv.hostPlatform; {
+stdenv:
+# set a few default values so we don't depend on what's exported from
+# hostPlatform from whatever nixpkgs set we are working against.
+with { isLinux = false; isWindows = false; isDarwin = false; isFreeBSD = false;
+       isOpenBSD = false; isNetBSD = false; isiOS = false; isAndroid = false;
+       isGhcjs = false; isAsterius = false; isHurd = false;
+       isx86 = false; isPowerPC = false; isAarch32 = false; isAarch64 = false;
+       isMips = false; isWasm = false; isJavaScript = false;
+       is32bit = false; is64bit = false; };
+with stdenv.hostPlatform; {
   os = if isLinux   then "Linux"   else
        if isWindows then "Windows" else
-       if isDarwin     then "Osx"     else
+       if isDarwin  then "Osx"     else
        if isFreeBSD then "Freebsd" else
        if isOpenBSD then "Openbsd" else
        if isNetBSD  then "Netbsd"  else
        if isHurd    then "Hurd"    else
        if isiOS     then "Ios"     else
        if isAndroid then "Android" else
+       if isGhcjs   then "Ghcjs"   else
+       if isAsterius then "Asterius" else
        throw "Unknown OS";
   arch = if isx86     && is32bit then "I386"    else
          if isx86     && is64bit then "X86_64"  else
@@ -16,5 +27,8 @@ stdenv: with stdenv.hostPlatform; {
          if isAarch32            then "Arm"     else
          if isAarch64            then "Aarch64" else
          if isMips               then "Mips"    else
+         if isWasm    && is32bit then "Wasm32"  else
+         if isWasm    && is64bit then "Wasm64"  else
+         if isJavaScript         then "JavaScript" else
          throw "Unknown Arch";
 }