First of all, change sys$mmap to take a struct SC_mmap_params since our sycsall calling convention can't handle more than 3 arguments. This exposed a bug in Syscall::invoke() needing to use clobber lists. It was a bit confusing to debug. :^)
It's nice to be able to identify mmap's in /proc/PID/vm.
This also meant I had to implement BSS (SHT_NOBITS) sections in ELFLoader. I also added an strerror() so we can print out what the errors are.
