__UNIX__ define is outdated

[rico-chet]

The __UNIX__ define seems to be very special to GCC or something. Clang doesn't define this. Causes build issues, possibly causes correctness issues.

 find -name '*.h' -o -name '*.c' -exec grep --with-filename __UNIX__ {} \;
./lib/rip_manager.c:#if __UNIX__
./lib/rip_manager.c:#if __UNIX__
./lib/rip_manager.c:#if __UNIX__
./lib/rip_manager.c:#if __UNIX__
./lib/threadlib.c:#elif __UNIX__
./lib/relaylib.c:#if __UNIX__
./lib/socklib.c:#if __UNIX__
./lib/socklib.c:#if __UNIX__
./lib/socklib.c:#if __UNIX__