Suggestion - macro to make multi-threaded calls single-threaded

[lipx1508]

Hello!
Just to warn before explaining that it's my first time opening an issue, so if I say a misconception, I have my mind open for this.

The proposal is making threaded calls like "async" and "await" have a macro to not use threads at all, like MUJS_SINGLETHREADED.
The most common method for making multi-threaded calls single-threaded is faking it, like how some OS's and kernels do, for example:

unsigned int thread_id; // ID of the thread

while (1) { // Loop example
    switch (thread_id) { // Executes call on thread
        case 0: ...
        case 1: ...
    }
}

I was going to make a pull request with more context and an in-practice application for it, but I'm not really sure if it would be viable giving the context.

Thanks for reading, have a good morning, afternoon or night :)