This test `gdb_test "stepi" "\r\nhandler .*"' in kill-after-signal.exp
performs a single-step, and deliver a signal (SIGUSR1) to inferior.
Software single step can not do that, because the next instruction
(start of handler) is unable to be determined.

This patch is to allow running this case only on x86 and x86_64, on
which hardware single step is supported.

OK?

-- 
Yao (齐尧)