[llvm] [WebAssembly] Use DebugValueManager only when subprogram exists (PR #77978)

[Heejin Ahn via llvm-commits]

aheejin wrote:

> I would imagine that practically speaking we could get nearly all of the benefits of the lookahead even with a limit in the hundreds of instructions or something. Maybe we could just pick the value based on how much faster it makes the example in the bug?

Yeah, I think I can run a little test with some sizable binaries on various lookahead limit values to see how debug coverage changes and decide on a number. Will do that as a follow-up.

https://github.com/llvm/llvm-project/pull/77978