[temporary patch from upstream PR] hw/riscv: Fix type conflict of GLib function pointers

This patch is temporary patch cherry-picked from the upstream PR. This should be removed once this is available on the upstream.

> qtest_set_command_cb passed to g_once should match GThreadFunc,
> which it does not.  But using g_once is actually unnecessary,
> because the function is called by riscv_harts_realize() under
> the Big QEMU Lock.
>
> Reported-by: Kohei Tokunaga <[email protected]>
> Signed-off-by: Paolo Bonzini <[email protected]>

Author: ktock

hw/riscv/riscv_hart.c

@@ -104,8 +104,11 @@ static bool csr_qtest_callback(CharBackend *chr, gchar **words)
 
 static void riscv_cpu_register_csr_qtest_callback(void)
 {
-    static GOnce once;
-    g_once(&once, (GThreadFunc)qtest_set_command_cb, csr_qtest_callback);
+    static bool first = true;
+    if (first) {
+        first = false;
+        qtest_set_command_cb(csr_qtest_callback);
+    }
 }
 #endif