Generate source map for target wasm32


I saw that recently, Rust got the ability to generate the source map for debug purposes when the target is WebAssembly (wasm32-unknown-unknown), see this PR.
I want to activate it but I find no option in cargo to generate it (even though the debug option is set to true in my Cargo.toml profiles).

It would be very useful for me since one of my code works when compiled to a normal binary but crash with the wasm version.

Faithfully yours,

The github account for the Mozilla author of the pull probably a good starting point to figuring out getting source maps built.
The source of demo