[compiler-rt] [ASan] Recognize WASI platform in sanitizer_platform.h (PR #139017)

[Derek Schuff via llvm-commits]

dschuff wrote:

/cc @sunfishcode @sbc100 
That reminds me we should think about upstreaming our Emscripten sanitizer implementation. 
@kateinoigakukun there may not be a huge amount of overlap with WASI since I suspect that the "OS" layers are more relevant here than the architecture, but it might be worth taking a look at our version [here](https://github.com/emscripten-core/emscripten/tree/main/system/lib/compiler-rt)

https://github.com/llvm/llvm-project/pull/139017