cp: -p should not fail if getxattrs fails

When running gnu `cp` with -p it ignores the failure when accessing `system.posix_acl_access`, uutils returns a non-zero exit code which breaks scripts.

```
getxattr("/dev/shm/foo", "system.posix_acl_access", 0x7ffd97504180, 132) = -1 EOPNOTSUPP (Operation not supported)
```