[llvm] Fix warnings while building llvm against emscripten for web assembly (PR #118262)

[Anutosh Bhat via llvm-commits]

anutosh491 wrote:

cc @sbc100 

Do these changes look reasonable to you now ? I think @whitequark approves. 
Obviously we might find work arounds here and there but shouldn't we cater specific configs needed by specific systems ?

I mean I see different setting based on checks like `if(APPLE)`, `If(MSVC)` etc

But if that's not the case, whatever workaround is there should be well documented somewhere. I've not had problems building llvm but then I see too warnings to ignore, hence in favour of such a change.


https://github.com/llvm/llvm-project/pull/118262