buildMozillaMach: apply upstream WASI SDK workaround for LLVM 19

I have no idea why this is necessary for us and why the upstream patch
doesn’t work, but this gets the Mozilla packages building on LLVM
19 in the meantime while we try to figure that out.

Closes: #352724

pkgs/applications/networking/browsers/firefox/common.nix

@@ -254,6 +254,25 @@ buildStdenv.mkDerivation {
       hash = "sha256-2IpdSyye3VT4VB95WurnyRFtdN1lfVtYpgEiUVhfNjw=";
     })
   ]
+  ++ [
+    # LLVM 19 turned on WASM reference types by default, exposing a bug
+    # that broke the Mozilla WASI build. Supposedly, it has been fixed
+    # upstream in LLVM, but the build fails in the same way for us even
+    # with LLVM 19 versions that contain the upstream patch.
+    #
+    # Apply the temporary patch Mozilla used to work around this bug
+    # for now until someone can investigate what’s going on here.
+    #
+    # TODO: Please someone figure out what’s up with this.
+    #
+    # See: <https://bugzilla.mozilla.org/show_bug.cgi?id=1905251>
+    # See: <https://github.com/llvm/llvm-project/pull/97451>
+    (fetchpatch {
+      name = "wasi-sdk-disable-reference-types.patch";
+      url = "https://hg.mozilla.org/integration/autoland/raw-rev/23a9f6555c7c";
+      hash = "sha256-CRywalJlRMFVLITEYXxpSq3jLPbUlWKNRHuKLwXqQfU=";
+    })
+  ]
   ++ extraPatches;
 
   postPatch = ''