[llvm] [WebAssembly] Disable multivalue emission temporarily (PR #82714)

[Thomas Lively via llvm-commits]

https://github.com/tlively approved this pull request.

Just to make sure I understand: we will still emit `multivalue` into the target features section if `-mmultivalue` is passed, but that will no longer affect codegen at all unless the new temporary flag is also passed?

https://github.com/llvm/llvm-project/pull/82714