Fixing the gcc-cross-wrapper; it failed after some changes related to breaking

dependencies with it. (I should never link ld.so with a NIX_LDFLAGS -rpath
forced)

I made vim, scummvm cross-build. I added prboom (that cross-builds).
Mplayer and elinks don't cross-build fine still, but are on the way.
The mplayer fails to build in a weird way; nix does not show either a gcc
error message or even the 'make' error message.

svn path=/nixpkgs/branches/stdenv-updates/; revision=23131

pkgs/development/libraries/SDL/default.nix

@@ -1,6 +1,7 @@
-{ stdenv, fetchurl, x11, libXrandr, pkgconfig
+{ stdenv, fetchurl, pkgconfig
 , openglSupport ? false, mesa ? null
 , alsaSupport ? true, alsaLib ? null
+, x11Support ? true, x11 ? null, libXrandr ? null
 , pulseaudioSupport ? true, pulseaudio ? null
 }:
 
@@ -8,10 +9,18 @@
 # PulseAudio.
 assert alsaSupport || pulseaudioSupport;
 
-assert openglSupport -> mesa != null;
+assert openglSupport -> (mesa != null && x11Support);
+assert x11Support -> (x11 != null && libXrandr != null);
 assert alsaSupport -> alsaLib != null;
 assert pulseaudioSupport -> pulseaudio != null;
 
+let
+  configureFlagsFun = attrs: ''
+        --disable-oss
+        --disable-x11-shared --disable-alsa-shared --enable-rpath --disable-pulseaudio-shared
+        ${if alsaSupport then "--with-alsa-prefix=${attrs.alsaLib}/lib" else ""}
+      '';
+in
 stdenv.mkDerivation rec {
   name = "SDL-1.2.14";
 
@@ -21,7 +30,7 @@ stdenv.mkDerivation rec {
   };
 
   # Since `libpulse*.la' contain `-lgdbm', PulseAudio must be propagated.
-  propagatedBuildInputs = [ x11 libXrandr ] ++
+  propagatedBuildInputs = stdenv.lib.optionals x11Support [ x11 libXrandr ] ++
     stdenv.lib.optional pulseaudioSupport pulseaudio;
 
   buildInputs = [ pkgconfig ] ++
@@ -31,11 +40,11 @@ stdenv.mkDerivation rec {
   # XXX: By default, SDL wants to dlopen() PulseAudio, in which case
   # we must arrange to add it to its RPATH; however, `patchelf' seems
   # to fail at doing this, hence `--disable-pulseaudio-shared'.
-  configureFlags = ''
-    --disable-oss
-    --disable-x11-shared --disable-alsa-shared --enable-rpath --disable-pulseaudio-shared
-    ${if alsaSupport then "--with-alsa-prefix=${alsaLib}/lib" else ""}
-  '';
+  configureFlags = configureFlagsFun { inherit alsaLib; };
+
+  crossAttrs = {
+      configureFlags = configureFlagsFun { alsaLib = alsaLib.hostDrv; };
+  };
 
   passthru = {inherit openglSupport;};