I'm not sure of any other runtimes for compiling C/C++ to WASM, no, sorry. The complaints I have are repeated on the bug tracker (possibly in more places too).
So I suspect there might some community projects because of the issues I'm raising. Let me know if you find any!
(Of course, there's also runtimes/compilers for Go, Rust, etc—I've not researched them enormously. I believe Go is much nicer to work with because its JS boilerplate is just a common bit of code you include, it's not built per-binary, which means it's much, much easier to understand and work with.)
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