ZeroMQ support for solo mining

Gets new blocks from daemon immediately without polling, saving ~0.5 seconds on average when daemon gets new block from the network. Also saves some CPU cycles because it doesn't need to poll daemon every second.

Testing: add "daemon-zmq-port": 28083 to xmrig's pool config in config.json and run ./monerod --testnet --zmq-pub tcp://127.0.0.1:28083

src/base/tools/bswap_64.h

@@ -0,0 +1,37 @@
+/* XMRig
+ * Copyright (c) 2018-2021 SChernykh   <https://github.com/SChernykh>
+ * Copyright (c) 2016-2021 XMRig       <https://github.com/xmrig>, <support@xmrig.com>
+ *
+ *   This program is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef XMRIG_BSWAP_64_H
+#define XMRIG_BSWAP_64_H
+
+#ifdef _MSC_VER
+
+#include <stdlib.h>
+#define bswap_64(x) _byteswap_uint64(x)
+
+#elif defined __GNUC__
+
+#define bswap_64(x) __builtin_bswap64(x)
+
+#else
+
+#include <byteswap.h>
+
+#endif
+
+#endif /* XMRIG_BSWAP_64_H */