one zombie process because it does not do the cleanup. For a long running
NIS/YP server, it will have lots of zombie processes on it. Fix that by
ignoring the SIGCHLD signal since we don't really care about the exit
status in this case.
PR: bin/91980
Reported by: Arjan van der Velde <dj_noresult at hotmail.com>
Submitted by: Jui-Nan Lin" <jnlin at csie.nctu.edu.tw>
Reviewed by: delphij
MFC after: 1 month
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