Don't undefine bzero()/bcopy().

This was causing build failures against external libraries that happened to use
them, unless silly hacks were added to the modules that used those headers.

Review: https://reviewboard.asterisk.org/r/2359/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@382292 65c4cc65-6c06-0410-ace0-fbb531ad65f3