Ensure that the default autoconf CFLAGS are not used.

A recent change to the configure script that allows the user to specify
CFLAGS and/or LDFLAGS to the script had the unfortunate side effect of
letting autoconf's default CFLAGS (-g -O2) feed in to the rest of the build
system, thereby overriding the DONT_OPTIMIZE setting in menuselect. That
problem is now corrected.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@217074 65c4cc65-6c06-0410-ace0-fbb531ad65f3