Big fixes in the cross build:

- Before this changes, cflags and ldflags for the native and the cross compiler
  got mixed. Not all the gcc-wrapper/gcc-cross-wrapper variables are
  independant now, but enough, I think.
- Fixed the generic stdenv expression, which did a big mess on buildInputs and
  buildNativeInputs. Now it distinguishes when there is a stdenvCross or not.
  Maybe we should have a single stdenv and forget about the stdenvCross
  adapter - this could end in a stdenv a bit complex, but simpler than the
  generic stdenv + adapter.
- Added basic support in pkgconfig for cross-builds: a single PKG_CONFIG_PATH
  now works for both the cross and the native compilers, but I think this
  should work well for most cases I can think of.
- I tried to fix the guile expression to cross-biuld; guile is built, but not
  its manual, so the derivation still fails. Guile requires patching to
  cross-build, as far as I understnad.
- Made the glibcCross build to be done through the usage of a
  gcc-cross-wrapper over the gcc-cross-stage-static, instead of using it
  directly.
- Trying to make physfs (a neverball dependency) cross build.
- Updated the gcc expression to support building a cross compiler without getting
  derivation variables mixed with those of the stdenvCross.

svn path=/nixpkgs/branches/stdenv-updates/; revision=18534

pkgs/os-specific/linux/kernel-headers/2.6.28.nix

@@ -14,7 +14,7 @@ stdenv.mkDerivation {
     sha256 = "0hifjh75sinifr5138v22zwbpqln6lhn65k8b57a1dyzlqca7cl9";
   };
 
-  crossConfig = if (cross != null) then cross.config else null;
+  targetConfig = if (cross != null) then cross.config else null;
 
   platform = 
     if cross != null then cross.arch else
@@ -37,7 +37,7 @@ stdenv.mkDerivation {
   '';
 
   buildPhase = ''
-    if test -n "$crossConfig"; then
+    if test -n "$targetConfig"; then
        export ARCH=$platform
     fi
     make mrproper headers_check