pointers in argv and envv in userland and use that together with
kern_execve() and exec_free_args() to implement linux_execve() for the
amd64/linux32 ABI without using the stackgap.
- Implement linux_nanosleep() using the recently added kern_nanosleep().
- Use linux_emul_convpath() instead of linux_emul_find() in
exec_linux_imgact_try().
Tested by: cokane
Silence on: amd64