wasm-emscripten : add minimal support for configure contribs and core
Nacl is now deprecated : cf. https://blog.chromium.org/2020/08/changes-to-chrome-app-support-timeline.html
This mr adds support for wasm32-emscripten, converting NACL bits when necessary, or removing them for compat, configure, contribs and core.
Edited by Mehdi Sabwat