we had been using a stub weak definition of `mprotect` in wasm/missing.c
so far, but wasi-sdk 23 added mprotect emulation to wasi-libc[^1], so the
emulation is now linked instead. However, the emulation doesn't support
PROT_NONE and fails with ENOSYS, so we need to avoid calling mprotect
completely on WASI.
[^1]: 7528b13170