stub out mmap/munmap/exit
stub out mmap/munmap/exit

They need special handling because they're implemented by
librumprun_base and not reachable via rump_syscall().

XXX: editing a generated file.  But can fix it properly when
the actual issue is fixed properly.

deferpanic/gorump,deferpanic/gorump,deferpanic/gorump,deferpanic/gorump,deferpanic/gorump,deferpanic/gorump,deferpanic/gorump,deferpanic/gorump