ci: Add stage3/4 diff to aarch64-linux-release script.

ci/aarch64-linux-release.sh

@@ -64,6 +64,22 @@ stage3-release/bin/zig build test docs \
   --zig-lib-dir "$PWD/../lib" \
   -Denable-tidy
 
+# Ensure that stage3 and stage4 are byte-for-byte identical.
+stage3-release/bin/zig build \
+  --prefix stage4-release \
+  -Denable-llvm \
+  -Dno-lib \
+  -Doptimize=ReleaseFast \
+  -Dstrip \
+  -Dtarget=$TARGET \
+  -Duse-zig-libcxx \
+  -Dversion-string="$(stage3-release/bin/zig version)"
+
+# diff returns an error code if the files differ.
+echo "If the following command fails, it means nondeterminism has been"
+echo "introduced, making stage3 and stage4 no longer byte-for-byte identical."
+diff stage3-release/bin/zig stage4-release/bin/zig
+
 # Ensure that updating the wasm binary from this commit will result in a viable build.
 stage3-release/bin/zig build update-zig1