log: do not use CONFIG_USER_ONLY

This decouples logging further from config-target.h

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

linux-user/main.c

@@ -3760,6 +3760,7 @@ static void handle_arg_log(const char *arg)
         qemu_print_log_usage(stdout);
         exit(EXIT_FAILURE);
     }
+    qemu_log_needs_buffers();
     qemu_set_log(mask);
 }