Using Nim's heap allocator on a pre-allocated memory region

[PMunch]

You could always use GCCs wrap functionality. I did an experiment where I 
wrapped `mmap` to make all the memory used by a Nim process shared so I could 
run a second program which loaded all the shared memory and allowed the two 
programs to pass memory addresses between them. But I guess you'd have to 
supply your own allocator for how to allocate pages in your fixed memory.