lib: replace deprecated overrideDerivation with overrideAttrs

overrideDerivation has been deprecated since 2019. The new
overrideAttrs properly handles the env attribute set used by
modern derivations to avoid the NIX_CFLAGS_COMPILE overlap
error between env and top-level derivation arguments.

modules/lib.nix

@@ -10,20 +10,16 @@ inputs.nixpkgs.lib.extend (
     lib = prev;
   in
   {
-    # stolen from: https://stackoverflow.com/a/42398526
     optimizeWithFlags =
       pkg: flags:
-      lib.overrideDerivation pkg (
-        old:
-        let
-          newflags = lib.foldl' (acc: x: "${acc} ${x}") "" flags;
-          oldflags = if (lib.hasAttr "NIX_CFLAGS_COMPILE" old) then "${old.NIX_CFLAGS_COMPILE}" else "";
-        in
-        {
-          NIX_CFLAGS_COMPILE = "${oldflags} ${newflags}";
-          # stdenv = pkgs.clang19Stdenv;
-        }
-      );
+      pkg.overrideAttrs (old: {
+        env = (old.env or { }) // {
+          NIX_CFLAGS_COMPILE =
+            (old.env.NIX_CFLAGS_COMPILE or old.NIX_CFLAGS_COMPILE or "")
+            + " "
+            + (lib.concatStringsSep " " flags);
+        };
+      });
 
     optimizePackage =
       pkg: