/dev/zero is missing

Please include the following in your bug report:

**Version of emscripten/emsdk:**
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.50 (047b82506d6b471873300a5e4d1e690420b582d0)
clang version 18.0.0 (https://github.com/llvm/llvm-project 14028ec0a62210d68a4dd7a046ac79c8c3b7727e)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: C:\emsdk\upstream\bin

```cpp
int fd = open("/dev/zero", O_RDONLY);
assert(fd != -1);
```