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

[Heejin Ahn via llvm-commits]

aheejin wrote:

@TerrorJack Oh, I wasn't aware this feature had active users, and thought this as mainly an internal issue. But good to know that you use it, and sorry for the inconvenience.

@tlively It is a little unclear to me how we define disruptions. What we caused in users like @TerrorJack's workflow can count as disruptions, but if we enable multivalue (either by default or at least when Wasm EH is used) and that reveals some untested parts in the toolchain, that might count as potential disruptions as well. 

If I run Emscripten tests with multivalue enabled, currently all Emscripten EH tests (or anything that use `invoke`s) fail, which is a problem if we enable multivalue by default but may be fine if we enable it only for Wasm EH. `invoke` failure itself can be probably fixed with a little effort. I also have 10+ more failures (whose failing reasons may or may not be grouped into a few) in Emscripten test suite that I have yet to investigate. So yeah, the backup plan can be, reverting this, investigating the current failures and fix them ;) which I hoped not to be blocked on. But maybe that's a better way in the long run?

I'll then revert this patch for now and investigate a little more on the failures.

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