[WebAssembly] Fix a few tests for WASI

[MaxDesiatov]

Disables/enables stdlib testing code appropriately when targeting WebAssembly/WASI.

This is a part of SR-9307 and #24684.

(cc @kateinoigakukun)

[gribozavr]

@swift-ci Please test and merge

[compnerd]

I really would prefer that you didn't do this change. WASI uses musl, not glibc, and there are user visible differences between the implementations. This is going to cause problems.

[MaxDesiatov]

@compnerd I can close the PR for now, but has anyone tried to support musl in the Swift infrastructure yet? Would a better approach be to support musl on say Linux directly before attempting to support it for the WASI target?

[kateinoigakukun]

@compnerd Do you mean we should replace these import statements with import Musl to match library name and actual library content?

[MaxDesiatov]

@kateinoigakukun Yes, that's would work best in my opinion too. Would be easiest to set this up for Linux first I think, I'm trying to build everything on Alpine to verify this.

[MaxDesiatov]

@compnerd this one will be either reverted or superseded with import Musl change that I'm actively working on right now. Sorry, wasn't sure if CI was actually stuck and whether it was going to merge it at all.