add pegtl to overlay for 2.91-dev

overlay.nix

@@ -89,6 +89,8 @@ let
       else prev.prefetch-npm-deps;
 
     nix-doc = prev.callPackage ./nix-doc/package.nix { withPlugin = false; };
+
+    pegtl = prev.callPackage ./pegtl.nix { };
   };
 in
   # Make the overlay idempotent, since flakes passing nixos modules around by

pegtl.nix

@@ -0,0 +1,23 @@
+{
+  stdenv,
+  cmake,
+  ninja,
+  fetchFromGitHub,
+}:
+
+stdenv.mkDerivation {
+  pname = "pegtl";
+  version = "3.2.7";
+
+  src = fetchFromGitHub {
+    repo = "PEGTL";
+    owner = "taocpp";
+    rev = "refs/tags/3.2.7";
+    hash = "sha256-IV5YNGE4EWVrmg2Sia/rcU8jCuiBynQGJM6n3DCWTQU=";
+  };
+
+  nativeBuildInputs = [
+    cmake
+    ninja
+  ];
+}