cloog-ppl: Move build inputs to nativeBuildInputs. This fixes cross-compilation since then we don't try to cross-compile Perl.

pkgs/development/libraries/cloog-ppl/default.nix

···
 
   propagatedBuildInputs = [ ppl ];
 
-  buildInputs = [ automake autoconf libtool ];
+  nativeBuildInputs = [ automake autoconf libtool ];
 
   patches = [ ./fix-ppl-version.patch ];