tests: add G_GNUC_PRINTF for various functions

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20221219130205.687815-6-berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/tests/qtest/libqmp.c b/tests/qtest/libqmp.c
index 2b08382..a89cab0 100644
--- a/tests/qtest/libqmp.c
+++ b/tests/qtest/libqmp.c
@@ -134,7 +134,7 @@
  * in the case that they choose to discard all replies up until
  * a particular EVENT is received.
  */
-static void
+static G_GNUC_PRINTF(4, 0) void
 _qmp_fd_vsend_fds(int fd, int *fds, size_t fds_num,
                   const char *fmt, va_list ap)
 {