Add missing <sys/select.h> include

`select()` may not be ambiently available for use on every platform

src/nix/daemon.cc

@@ -24,6 +24,7 @@
 #include <sys/stat.h>
 #include <sys/socket.h>
 #include <sys/un.h>
+#include <sys/select.h>
 #include <errno.h>
 #include <pwd.h>
 #include <grp.h>