provide libz.so.1 in the nix-dev-shell

`libz.so.1` is needed for some (?) things...

i personally found myself in need of it when running `x t linkchecker`,
which failed when running cargo build script or something.

although there are also mentions of rustc itself needing it:
<NixOS/nixpkgs#92946>

Author: WaffleLapkin

src/tools/nix-dev-shell/flake.nix

@@ -24,9 +24,8 @@
           # Avoid creating text files for ICEs.
           RUSTC_ICE = "0";
           # Provide `libstdc++.so.6` for the self-contained lld.
-          LD_LIBRARY_PATH = "${with pkgs; lib.makeLibraryPath [
-            stdenv.cc.cc.lib
-          ]}";
+          # Provide `libz.so.1`.
+          LD_LIBRARY_PATH = "${with pkgs; lib.makeLibraryPath [stdenv.cc.cc.lib zlib]}";
         };
       }
     );

src/tools/nix-dev-shell/shell.nix

@@ -13,7 +13,6 @@ pkgs.mkShell {
   # Avoid creating text files for ICEs.
   RUSTC_ICE = "0";
   # Provide `libstdc++.so.6` for the self-contained lld.
-  LD_LIBRARY_PATH = "${with pkgs; lib.makeLibraryPath [
-    stdenv.cc.cc.lib
-  ]}";
+  # Provide `libz.so.1`
+  LD_LIBRARY_PATH = "${with pkgs; lib.makeLibraryPath [stdenv.cc.cc.lib zlib]}";
 }