Split usermem package to help remove syserror dependency in go_marshal. New hostarch package contains code not dependent on syserror. PiperOrigin-RevId: 365651233
PiperOrigin-RevId: 331940975
PiperOrigin-RevId: 323491461
Example: epoll_ctl(0x3 anon_inode:[eventpoll], EPOLL_CTL_ADD, 0x6 anon_inode:[eventfd], 0x7efe2fd92a80 {events=EPOLLIN|EPOLLOUT data=0x10203040506070a}) = 0x0 (4.411µs) epoll_wait(0x3 anon_inode:[eventpoll], 0x7efe2fd92b50 {{events=EPOLLOUT data=0x102030405060708}{events=EPOLLOUT data=0x102030405060708}{events=EPOLLOUT data=0x102030405060708}}, 0x3, 0xffffffff) = 0x3 (29.891µs) PiperOrigin-RevId: 296258146