ALLJOYN-2137: Remove the '-fno-rtti' option for Linux and Darwin builds.

Only code compiled with '-fno-rtti' can link to a library compiled with
'-fno-rtti'.  However, code built with '-no-rtti' can link to a library
compiled without '-fno-rtti'.  By removing that option, we don't force users of
liballjoyn to also use '-fno-rtti', thus allowing them to use RTTI if they so
choose.

Change-Id: I78950a7af91bce5cd6789f66ec145bc924daa749