Runtime/Compile error on iOS 14.x

`SharedArrayBuffer` is only supported after iOS 15.2, so I tried using `core-st`. I tested the same script on desktop and it works fine: the webpage freezes during execution, but the console shows its working alright and the output comes out fine. On iOS itself however I'm getting a Runtime/Compile error when loading `core-st`:
```
RuntimeError: abort(CompileError: WebAssembly.Module doesn't parse at byte 62327: invalid section). Build with -s ASSERTIONS=1 for more info. (evaluating 'new WebAssembly.RuntimeError("abort("+a+"). Build with -s ASSERTIONS=1 for more info.")')
```
This error message in particular came from `@ffmpeg/core-st@0.11.1` but I also tried `0.11.0`, and also my fork of the core `@willyjl/ffmpeg.wasm-core-vistab-st`, and they also produced the same error (if I remember correctly `0.11.1` and `0.11.0` both had the same byte offset, while my `vidstab` fork had an (understandably) slightly different number).

I would look into this myself but I know very little of this low level stuff, so I'll just link some things I found that look similar to this issue for reference:
- https://github.com/emscripten-core/emscripten/issues/15673
- https://github.com/emscripten-core/emscripten/issues/17609