8316566: RISC-V: Zero extended narrow oop passed to Atomic::cmpxchg

Reviewed-by: goetz
Backport-of: 9ffec67a3f2dada329a9887338c570424a79e7f8

src/hotspot/os_cpu/linux_riscv/orderAccess_linux_riscv.hpp

@@ -37,7 +37,7 @@ inline void OrderAccess::storestore() { release(); }
 inline void OrderAccess::loadstore()  { acquire(); }
 inline void OrderAccess::storeload()  { fence(); }
 
-#define FULL_MEM_BARRIER  __sync_synchronize()
+#define FULL_MEM_BARRIER  __atomic_thread_fence(__ATOMIC_SEQ_CST);
 #define READ_MEM_BARRIER  __atomic_thread_fence(__ATOMIC_ACQUIRE);
 #define WRITE_MEM_BARRIER __atomic_thread_fence(__ATOMIC_RELEASE);