Optimization O3 fails when importing Wasi functions

The implementation of PThreadFS imports Wasi functions such as `fd_write()`. Unfortunately, this fails under optimization level `-O3`. Under optimization level `-O2`, everything works well. Is there a way to avoid this issue?

Minimal example
```
#include
#include

EM_IMPORT(fd_close) __wasi_errno_t env_fd_close(__wasi_fd_t fd);

int main() {
env_fd_close(1);
return 0;
}
```
Compile with `emcc -o o3bug.html o3bug.cpp -O3`, then instantiation fails with
```
RuntimeError: Aborted(LinkError: WebAssembly.instantiate(): Import #0 module="a" function="a" error: function import requires a callable). Build with -s ASSERTIONS=1 for more info.
```
Using Emsdk 3.1.3, Chrome 98.