fusee-launcher: respect targetPrefix of arm-embedded toolchain

pkgs/development/tools/fusee-launcher/default.nix

···
 , makeWrapper
 } :
 
+let
+  arm-embedded-cc = pkgsCross.arm-embedded.buildPackages.gcc;
+in
+
 stdenv.mkDerivation {
   pname = "fusee-launcher";
   version = "unstable-2018-07-14";
···
     sha256 = "1pqkgw5bk0xcz9x7pc1f0r0b9nsc8jnnvcs1315d8ml8mx23fshm";
   };
 
+  makeFlags = [
+    "CROSS_COMPILE=${arm-embedded-cc.targetPrefix}"
+  ];
+
   installPhase = ''
     mkdir -p $out/bin $out/share
     cp fusee-launcher.py $out/bin/fusee-launcher
···
       --prefix PYTHONPATH : "$PYTHONPATH:$(toPythonPath $out)"
   '';
 
-  nativeBuildInputs = [ pkgsCross.arm-embedded.buildPackages.gcc makeWrapper python3Packages.wrapPython ];
+  nativeBuildInputs = [ arm-embedded-cc makeWrapper python3Packages.wrapPython ];
   buildInputs = [ python3 python3Packages.pyusb ];
   pythonPath = with python3Packages; [ pyusb ];