hwclock: force LONG_OPTS, stop accepting non-compatible -t

function                                             old     new   delta
hwclock_main                                         576     579      +3
.rodata                                           105404  105349     -55
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 3/-55)             Total: -52 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>