nix(pkgs): patch wabt with WebAssembly/wabt#2744

`return_call_indirect` under `table64` rejects an i64 table-index in
upstream wabt, while the matching `call_indirect` accepts it — a
clean asymmetry in the validator. The patched wabt mirrors the
working `OnCallIndirect` plumbing in `OnReturnCallIndirect` (4 lines
+ a regression test). With the patch, our `tailcall` bench's
`return_call_indirect` sites validate clean and the temporary
`tailcall.valid.{ok,ret.ok}` files this PR introduced are no longer
needed — drop them.

Patch is fetched from the open upstream PR via `fetchpatch`. Drop
this overlay (and the two-line `__intentionallyOverridingVersion`
shim) once the fix lands and nixpkgs picks it up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ggreif

nix/pkgs.nix

@@ -59,5 +59,24 @@
 
     # ic-wasm
     (self: super: { ic-wasm = import ./ic-wasm.nix self; })
+
+    # wabt with WebAssembly/wabt#2744 patched in (return_call_indirect
+    # + table64 validator fix). Patches nixpkgs's wabt source rather
+    # than swapping it out so the third_party/* submodules nixpkgs
+    # already fetches stay intact. Drop this overlay once #2744 lands
+    # and propagates to nixpkgs.
+    (self: super: {
+      wabt = super.wabt.overrideAttrs (old: {
+        patches = (old.patches or []) ++ [
+          (super.fetchpatch {
+            name = "wabt-pr-2744-return_call_indirect-table64.patch";
+            url = "https://github.com/WebAssembly/wabt/pull/2744.patch";
+            hash = "sha256-RzGaVgitOcv2KkHV1HT77A2WLPwJtBxYB9rS0u42tko=";
+          })
+        ];
+        version = "${old.version}-pre-2744";
+        __intentionallyOverridingVersion = true;
+      });
+    })
   ];
 }