Also print mmap return value and error code #ifdef DEBUG_MMAP.

don't check the value of retval in netbsd32_mmap() if sys_mmap()
was not successful.

move mmap(), compat 40 mount(), pipe() and getfh() into their own files
as the implementation is non trivial or is compat. mark old mount()
properly instead of manually #if'ing ito to ENOSYS.