treewide: Add lots of platforms to packages with no meta

Build-tested on x86_64 Linux and on Darwin.

pkgs/development/libraries/java/saxon/default.nix

@@ -10,4 +10,8 @@ stdenv.mkDerivation {
 
   inherit unzip;
   buildInputs = [unzip];
+
+  meta = {
+    platforms = stdenv.lib.platforms.unix;
+  };
 }

pkgs/development/libraries/java/saxon/default8.nix

@@ -19,4 +19,8 @@ exec ${jre}/bin/java -jar $out/saxon8.jar \"\\$@\"
 EOF
     chmod a+x $out/bin/saxon8
   ";
+
+  meta = {
+    platforms = stdenv.lib.platforms.unix;
+  };
 }