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

[Cheng Shao via llvm-commits]

TerrorJack wrote:

one small input from downstream user: the ghc wasm backend distributes its own wasi-sdk fork based on llvm trunk and we do enable multi-value by default, including the experimental mv abi in c, in the hope of uncovering more bugs for the sake of upstream as well as rest of the wasm ecosystem. other than #71124, multi value as well as the new abi hasn't caused us other trouble so far.

this patch looks easy enough to workaround in our downstream builds so we can continue to test against the mv abi without needing to figure out how to pass that flag all the way up from the clang driver, etc. still, i'm rather surprised such a significant change was proposed and merged in such a short timeline, with absolutely no community notice or grace period :/

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