This is my proposal for porting D runtime to WebAssembly. I would like to ask you to review it. You can find it here: https://gist.github.com/skoppe/7617ceba6afd67b2e20c6be4f922725d
An alternative idea, would be to use emscriptens fork of musl to have a full C-library. AFAIK this includes threading.
LLVM is supposed to support TLS in wasm since version 9.
