Handle FPE and BUS scenarios in the ATF t_trapsignal tests
These crash signals are crucial for proper handling of abnormal conditions
in a program. The additional purpose of these tests it to assure the proper
handling of these signals for the coming ptrace(2)-related changes in the
signal routing code.
Add a stub for ILL scenarios.
All tests pass (on amd64).
The shell ATF script contains duplicated code. There should be a way to
deduplicate it, without rewrite to C.
Sponsored by <The NetBSD Foundation>
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