treewide: Use *Platform.extensions

pkgs/tools/networking/eggdrop/default.nix

@@ -1,9 +1,5 @@
 { stdenv, fetchFromGitHub, tcl }:
 
-let
-  shlib = if stdenv.isDarwin then "dylib" else "so";
-in
-
 stdenv.mkDerivation rec {
   name = "eggdrop-${version}";
   version = "1.6.21-nix1";
@@ -29,7 +25,7 @@ stdenv.mkDerivation rec {
   '';
 
   configureFlags = [
-    "--with-tcllib=${tcl}/lib/lib${tcl.libPrefix}.${shlib}"
+    "--with-tcllib=${tcl}/lib/lib${tcl.libPrefix}${stdenv.hostPlatform.extensions.sharedLibrary}"
     "--with-tclinc=${tcl}/include/tcl.h"
   ];