Ok. The issue is: bad limit handling for COMPAT_NETBSD32.

Things like VM_DEFAULT_ADDRESS (used to determine the address to load
the ELF loader at) only deal with the default, native (64bit) limits.
The code got away with this in the past, because MAXDSIZ on amd64 was
below the 32bit limits. But now, it's 8G, things overflow, and come
up with the wrong address to map the ELF loader.

It's fixable, but it needs a little work. I'll fix it later this week.

- Frank