[clang] [llvm] Conditionalize use of POSIX features missing on WASI/WebAssembly (PR #92677)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Sorry for not responding sooner, but I think this approach makes sense to me. It's basically similar to autoconf where we're checking whether a feature is supported and guarding against it.

One concern I have is that someone adding new code may think they need to come up with fallback behavior in case a feature isn't available (e.g., "how do I do this if I don't have `setjmp`?) and it would be nice if we could find a way to make it clear that they are not responsible for coming up with that fallback behavior. (Mostly worried about folks doing a bunch of heavy lifting before submitting a PR only to hear during review "you didn't need to do that, please pull it out because we don't have a way to test it".)

https://github.com/llvm/llvm-project/pull/92677