tinyxml2: fix cross compilation

- use native unzip
- add target prefix to LD

pkgs/development/libraries/tinyxml/2.6.2.nix

@@ -23,14 +23,14 @@ in stdenv.mkDerivation {
     ./2.6.2-cxx.patch
   ];
 
-  preConfigure = "export LD=${if stdenv.isDarwin then "clang++" else "g++"}";
+  preConfigure = "export LD=${stdenv.cc.targetPrefix}c++";
 
   hardeningDisable = [ "format" ];
 
   NIX_CFLAGS_COMPILE =
     stdenv.lib.optionalString stdenv.isDarwin "-mmacosx-version-min=10.9";
 
-  buildInputs = [ unzip ];
+  nativeBuildInputs = [ unzip ];
   buildPhase = ''
     # use STL (xbmc requires it)
     sed '1i#define TIXML_USE_STL 1' -i tinyxml.h