Don't redefine _POSIX_C_SOURCE if already defined, use single code path in rtpp_glitch_realpath(), so that we don't have to "glitch" glitching code.
Don't redefine _POSIX_C_SOURCE if already defined,
use single code path in rtpp_glitch_realpath(), so that we
don't have to "glitch" glitching code.

sippy/rtpproxy,dsanders11/rtpproxy,sippy/rtpproxy,dsanders11/rtpproxy,dsanders11/rtpproxy,sippy/rtpproxy