Update xnnpack.cmake for WASM build (#24860)
### Description
This change updates the xnnpack.cmake file to reflect changes in
XNNPACK's CMake and Bazel build files.
### Motivation and Context
Fixes the WASM build issue with --use_xnnpack
(https://github.com/microsoft/onnxruntime/issues/23460).
---------
Co-authored-by: Yulong Wang <7679871+fs-eire@users.noreply.github.com>
