Properly detect launchd

Asterisk was a little too pro-active in claiming that it found launchd. On
systems without launchd - such as FreeBSD - this resulted in certain items
in Asterisk that conflict with launchd to not be selectable, such as
res_timing_kqueue.

(closes issue ASTERISK-20749)
Reported by: Oleg Baranov
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Merged revisions 381847 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 381848 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@381869 65c4cc65-6c06-0410-ace0-fbb531ad65f3