`icu4c_wasm.patch` is build by :
- Copying config.sub from liblzma source as new version of config.sub there
knows about wasm architecture.
- Copying `mh-linux` on `mh-unknown` as specified in (origin) `mh-unknown`.
This is because icu4c configure doesn't detect `emscripten` platform and
"fallback" to `mh-unknown`.
Matthieu Gautier