Failed to generate WASI socket API in standalone Wasm

Please include the following in your bug report:

**Description**
Hi, I try to compile a simple server written by C(only contains `socket()`, `recvfrom()` and `sendto()`) to a standalone Wasm using Emscripten.
However, I find in the compiled Wasm file, the import functions related to socket API are not from the WASI interface but from custom `env`, thus it cannot be executed in a standalone Wasm runtime.
Should I add some options of Emscripten when I compile it?
Thank you!

**Version of emscripten/emsdk:**
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.24 (68a9f990429e0bcfb63b1cde68bad792554350a5)
clang version 16.0.0 (https://github.com/llvm/llvm-project 277c382760bf9575cfa2eac73d5ad1db91466d3f)
Target: wasm32-unknown-emscripten
Thread model: posix

**Failing command line in full:**
Both command lines failed to generate WASI socket API.
```
emcc -sENVIRONMENT=shell -O2 -sSTANDALONE_WASM -sERROR_ON_UNDEFINED_SYMBOLS=0 server.c -o server.wasm
emcc -sENVIRONMENT=shell -O2 -sSTANDALONE_WASM -sERROR_ON_UNDEFINED_SYMBOLS=0 -lwebsocket.js -sPROXY_POSIX_SOCKETS server.c -o server.wasm

```