X11 - XQueryTree produces "illegal storage acess" segfault when run

[Araq]

    numChildrenReturn: Pcuint
    
    
    
    Run

is wrong, you need to allocate storage for it. I would use:
    
    
    numChildrenReturn: cuint
    
    
    
    Run

And then `addr(numChildrenReturn)` in the call to `XQueryTree`.

And frankly, such a mistake indicates that you're not ready for X11's low level 
API. Read some tutorial about Nim's memory model and what to watch out for when 
interfacing with C.