Guard realtime functions with _XOPEN_REALTIME, and remove a bogus debug line.
Guard realtime functions with _XOPEN_REALTIME, and remove a bogus debug line.

zevv/luaposix,ardje/luaposix,rrthomas/luaposix,jimmyharris/luaposix,luaposix/luaposix,snegovick/luaposix,zevv/luaposix,rrthomas/luaposix,snegovick/luaposix,jimmyharris/luaposix,ardje/luaposix