epoll_ctl warns for uninitialized padding on non-amd64 64bit arches

epoll_ctl warns for uninitialized padding on non-amd64 64bit arches

struct vki_epoll_event is packed on x86_64, but not on other 64bit
arches. This means that on 64bit arches there can be padding in the
epoll_event struct. Seperately the data field is only used by user
space (which might not set the data field if it doesn't need to).

Only check the events field on epoll_ctl. But assume both events
and data are both written to by epoll_[p]wait (exclude padding).

https://bugs.kde.org/show_bug.cgi?id=422623