`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`.
This commit add a first version code to build a flatpak of kiwix-desktop.
It is mainly based on the PR #254 of @birros (hence he is the author of this commit)
However there is some differences :
- I (@mgautier) create a new builder to run the flatpak build instead of using a new
dependency.
- Use the flatpak platform to install org.kde.Platform and org.kde.Sdk
This code version doesn't correctly work but I wanted to commit the birros' code
without too many modification (even if there is a lot).