util: unify implementation of NOP signal handler

This is highly complex code after all, we really should make sure to
only keep one implementation of this extremely difficult function
around.

src/basic/util.c

@@ -6916,3 +6916,7 @@ int receive_one_fd(int transport_fd, int flags) {
 
         return *(int*) CMSG_DATA(found);
 }
+
+void nop_signal_handler(int sig) {
+        /* nothing here */
+}