Allow some core dump-related fields to be overridden. This allows
core dumps to work correctly for x32.
Signed-off-by: H. Peter Anvin <hpa@zytor.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Roland McGrath <roland@redhat.com> Cc: Oleg Nesterov <oleg@redhat.com>