Use standard RNG

The custom random number generator can now be replaced with a C++11
RNG. This greatly improves the reliability and trustworthiness of it.

In addition to this, the conversion of the RNG to a thread-local object
removes the race condition that was present in the previous
implementation. It also theoretically improves performance by a tiny bit.

include/maxscale/random.h

@@ -0,0 +1,28 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2022-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <maxscale/cdefs.h>
+
+MXS_BEGIN_DECLS
+
+/**
+ * @brief Return a pseudo-random number
+ *
+ * Return a pseudo-random number that satisfies major tests for random sequences.
+ *
+ * @return A random number
+ */
+unsigned int mxs_random(void);
+
+MXS_END_DECLS