importd: remove IN_SET to avoid ambiguity

clang warns:
../src/import/importd.c:254:70: warning: 'break' is bound to current loop, GCC binds it to the enclosing loop [-Wgcc-compat]
                while ((e < t->log_message + t->log_message_size) && IN_SET(*e, 0, '\n'))
                                                                     ^
Let's just play it safe and not use IN_SET here.

src/import/importd.c

@@ -251,7 +251,7 @@ static void transfer_send_logs(Transfer *t, bool flush) {
                 n = strndup(t->log_message, e - t->log_message);
 
                 /* Skip over NUL and newlines */
-                while ((e < t->log_message + t->log_message_size) && IN_SET(*e, 0, '\n'))
+                while (e < t->log_message + t->log_message_size && (*e == 0 || *e == '\n'))
                         e++;
 
                 memmove(t->log_message, e, t->log_message + sizeof(t->log_message) - e);