Add test.
Add test.

With this change to the test but not the fix in the previous commit, running
os_signal_SUITE with emulator arg +Bd or +Bi will fail (BEAM will die with a
signal, which is not the best way to fail a test, but we don't have a shell
test suite to catch it).

To confirm, you can use ts, with
`ts:run(emulator, os_signal_SUITE, [{vars, [{erl_start_args, "+Bd"}]}]).`.

jj1bdx/otp,mikpe/otp,bjorng/otp,getong/otp,dgud/otp,g-andrade/otp,getong/otp,bjorng/otp,dgud/otp,getong/otp,g-andrade/otp,mikpe/otp,potatosalad/otp,isvilen/otp,dgud/otp,rlipscombe/otp,vinoski/otp,mikpe/otp,isvilen/otp,jj1bdx/otp,ferd/otp,getong/otp,erlang/otp,erlang/otp,ferd/otp,erlang/otp,rlipscombe/otp,vinoski/otp,rlipscombe/otp,vinoski/otp,dumbbell/otp,uabboli/otp,potatosalad/otp,vinoski/otp,g-andrade/otp,emacsmirror/erlang,mikpe/otp,getong/otp,g-andrade/otp,isvilen/otp,uabboli/otp,dgud/otp,dgud/otp,erlang/otp,dumbbell/otp,dgud/otp,emacsmirror/erlang,rlipscombe/otp,potatosalad/otp,isvilen/otp,isvilen/otp,jj1bdx/otp,vinoski/otp,jj1bdx/otp,dgud/otp,g-andrade/otp,potatosalad/otp,jj1bdx/otp,bjorng/otp,g-andrade/otp,erlang/otp,erlang/otp,isvilen/otp,bjorng/otp,vinoski/otp,mikpe/otp,dumbbell/otp,mikpe/otp,vinoski/otp,ferd/otp,jj1bdx/otp,potatosalad/otp,emacsmirror/erlang,jj1bdx/otp,bjorng/otp,getong/otp,vinoski/otp,potatosalad/otp,jj1bdx/otp,bjorng/otp,rlipscombe/otp,erlang/otp,isvilen/otp,uabboli/otp,g-andrade/otp,ferd/otp,uabboli/otp,emacsmirror/erlang,vinoski/otp,rlipscombe/otp,getong/otp,uabboli/otp,dumbbell/otp,bjorng/otp,rlipscombe/otp,isvilen/otp,dumbbell/otp,emacsmirror/erlang,ferd/otp,uabboli/otp,emacsmirror/erlang,erlang/otp,isvilen/otp,potatosalad/otp,g-andrade/otp,mikpe/otp,erlang/otp,potatosalad/otp,g-andrade/otp,erlang/otp,mikpe/otp,vinoski/otp,potatosalad/otp,bjorng/otp,getong/otp,dgud/otp,ferd/otp,isvilen/otp,dumbbell/otp,bjorng/otp,emacsmirror/erlang,dumbbell/otp,dgud/otp,dumbbell/otp,emacsmirror/erlang,rlipscombe/otp,ferd/otp,rlipscombe/otp,getong/otp,mikpe/otp,rlipscombe/otp,uabboli/otp,emacsmirror/erlang,dgud/otp,jj1bdx/otp,ferd/otp,dumbbell/otp,potatosalad/otp,dumbbell/otp,emacsmirror/erlang,getong/otp,jj1bdx/otp,mikpe/otp,ferd/otp,uabboli/otp,bjorng/otp,g-andrade/otp,uabboli/otp