GCC 4.5: Patch the spec string for GNU/Hurd to add the right `-I' flags.

svn path=/nixpkgs/trunk/; revision=21934

pkgs/development/compilers/gcc-4.5/default.nix

@@ -143,6 +143,27 @@ stdenv.mkDerivation ({
     ++ optional langVhdl ./ghdl-ortho-cflags.patch
     ;
 
+  postPatch =
+    if (stdenv.system == "i586-pc-gnu"
+        || (cross != null && cross.config == "i586-pc-gnu"
+            && libcCross != null))
+    then
+      # On GNU/Hurd glibc refers to Hurd & Mach headers so add the right `-I'
+      # flags to the default spec string.
+      let
+        libc = if cross != null then libcCross else stdenv.glibc;
+        config_h = "gcc/config/i386/gnu.h";
+        extraCPPSpec =
+          concatStrings (intersperse " "
+                          (map (x: "-I${x}/include")
+                               libc.propagatedBuildInputs));
+      in
+        '' echo "augmenting \`CPP_SPEC' in \`${config_h}' with \`${extraCPPSpec}'..."
+           sed -i "${config_h}" \
+               -es'|CPP_SPEC *"\(.*\)$|CPP_SPEC "${extraCPPSpec} \1|g'
+        ''
+    else null;
+
   inherit noSysDirs profiledCompiler staticCompiler langJava crossStageStatic
     libcCross crossMingw;