Keep/separate out a list of symbols that are only stubs

[brettcannon]

Probably one of the biggest headaches in keeping CPython compatible with WASI is tracking the stubs that suddenly turn on "new" functionality thanks to configure discovering the new symbol. Having a list of the stubs (or https://github.com/WebAssembly/wasi-libc/blob/main/expected/wasm32-wasip2/defined-symbols.txt somehow delineating what are stubs) would be great as I can then turn off those function explicitly in the config.site file.