fix the case where menuselect.makeopts is getting generated in the same run of

"make" as the current build and some of the MENUELSELECT_CFLAGS are set in the
user or global level asterisk.makeopts file


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@36192 65c4cc65-6c06-0410-ace0-fbb531ad65f3