glibc: setting --enable-kernel=2.6.35

It was taking 2.4.0 as default, therefore, not using syscalls over 2.4.0
We may see performance improvements (openat, ...)

pkgs/development/libraries/glibc/2.13/common.nix

@@ -110,6 +110,8 @@ stdenv.mkDerivation ({
     (if profilingLibraries
      then "--enable-profile"
      else "--disable-profile")
+  ] ++ stdenv.lib.optionals (cross == null) [
+    "--enable-kernel=${kernelHeaders.versionForGlibc}"
   ] ++ stdenv.lib.optionals (cross != null) [
     (if cross.withTLS then "--with-tls" else "--without-tls")
     (if cross.float == "soft" then "--without-fp" else "--with-fp")

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

@@ -59,4 +59,8 @@ stdenv.mkDerivation {
       ln -s asm $out/include/asm-x86
     fi
   '';
+
+  passthru = {
+    versionForGlibc = "2.6.35";
+  };
 }