ensure that if a .i file (preprocessed source) is present, the .o file is made...

ensure that if a .i file (preprocessed source) is present, the .o file is made from it, not from the .c file (this only works because GNU makes respects the order the rules are defined)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@157167 65c4cc65-6c06-0410-ace0-fbb531ad65f3