xbursttools: Fix eval at least so tests pass

pkgs/tools/misc/xburst-tools/default.nix

···
 { stdenv, fetchgit, libusb, libusb1, autoconf, automake, confuse, pkgconfig
-, gccCross ? null }:
+, gccCross ? null, crossPrefix
+}:
 
 let
   version = "2011-12-26";
···
   '';
 
   configureFlags = if gccCross != null then
-    "--enable-firmware CROSS_COMPILE=${gccCross.crossConfig}-"
+    "--enable-firmware CROSS_COMPILE=${crossPrefix}-"
     else "";
 
   # Not to strip cross build binaries (this is for the gcc-cross-wrapper)

pkgs/top-level/all-packages.nix

···
 
   x11_ssh_askpass = callPackage ../tools/networking/x11-ssh-askpass { };
 
-  xbursttools = assert stdenv ? glibc; callPackage ../tools/misc/xburst-tools {
+  xbursttools = assert stdenv ? glibc; callPackage ../tools/misc/xburst-tools rec {
     # It needs a cross compiler for mipsel to build the firmware it will
     # load into the Ben Nanonote
+    crossPrefix = "mipsel-unknown-linux";
     gccCross =
       let
         pkgsCross = nixpkgsFun {
           # Ben Nanonote system
           crossSystem = {
-            config = "mipsel-unknown-linux";
+            config = crossPrefix;
             bigEndian = true;
             arch = "mips";
             float = "soft";
···
           };
         };
       in
-        pkgsCross.gccCrossStageStatic;
+        pkgsCross.buildPackages.gccCrossStageStatic;
   };
 
   xclip = callPackage ../tools/misc/xclip { };