RandomX fixes

Intel JCC erratum fix and various other improvements, see more here: https://www.phoronix.com/scan.php?page=article&item=intel-jcc-microcode&num=1

src/backend/common/Workers.cpp

@@ -109,6 +109,11 @@ void xmrig::Workers<T>::start(const std::vector<T> &data)
 
     for (Thread<T> *worker : m_workers) {
         worker->start(Workers<T>::onReady);
+
+        // This sleep is important for optimal caching!
+        // Threads must allocate scratchpads in order so that adjacent cores will use adjacent scratchpads
+        // Sub-optimal caching can result in up to 0.5% hashrate penalty
+        std::this_thread::sleep_for(std::chrono::milliseconds(20));
     }
 }