zsh: enable function subdirs

and patch script shebangs

pkgs/shells/zsh/default.nix

@@ -45,6 +45,7 @@ stdenv.mkDerivation {
     "--enable-pcre"
     "--enable-zshenv=${placeholder "out"}/etc/zshenv"
     "--disable-site-fndir"
+    "--enable-function-subdirs"
   ] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform && !stdenv.hostPlatform.isStatic) [
     # Also see: https://github.com/buildroot/buildroot/commit/2f32e668aa880c2d4a2cce6c789b7ca7ed6221ba
     "zsh_cv_shared_environ=yes"
@@ -112,6 +113,10 @@ EOF
   '';
   # XXX: patch zsh to take zwc if newer _or equal_
 
+  postFixup = ''
+    HOST_PATH=$out/bin:$HOST_PATH patchShebangs --host $out/share/zsh/*/functions
+  '';
+
   meta = {
     description = "The Z shell";
     longDescription = ''