Xcode produces XPC service which crashes on startup

A XPC service is not a stand-alone app, it needs to be launched by someone else is a specific way. Either by directly by launchd, or as a result of a request by an app.

That may be. But this can never work with illegal op-codes. That's why I'm reporting. The implementation problem may be related to this:

https://stackoverflow.com/questions/59080105/illegal-hardware-instruction-from-very-simple-code

It tested this code on the Macintosh using clang from mentioned Xcode version. Can confirm:

int proveit()
{
    unsigned int n = 0;
    while (1) n++;
    return 0;
}

int main()
{
    proveit();
    return 0;
}

This is delivering:

$ clang -O -o noway noway.c
$ ./noway
[1]    23086 illegal hardware instruction  ./noway