ts/kill/decode: consider arch dependent signum/name association

ts/kill/decode: consider arch dependent signum/name association

In the original code, the signal bits passed to the decode test were
sampled on x86_64. As reported in #3774, the association between signal
number and its name is architecture dependent.

With this change, the test case calculates the signal bits from signal
names at runtime instead of hardcoding.

Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://github.com/util-linux/util-linux/issues/3774
Signed-off-by: Masatake YAMATO <yamato@redhat.com>