Remove the `--no-threads` workaround for wasm targets.
Remove the `--no-threads` workaround for wasm targets.

Remove `--no-threads` from the wasm-ld command-line, which was a
workaround for [an old bug] which was fixed in LLVM 9.0, and is
no longer needed.

Also, the `--no-threads` option has been [removed upstream].

[an old bug]: https://bugs.llvm.org/show_bug.cgi?id=41508
[removed upstream]: https://reviews.llvm.org/D76885

aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust