Define wc_store_fence for riscv (#1475)

[ROCm/rccl commit: c6c7b6db98]

projects/rccl/src/include/gdrwrap.h

@@ -41,7 +41,7 @@ static inline void wc_store_fence(void) { asm volatile("sync") ; }
 #elif defined(__x86_64__)
 #include <immintrin.h>
 static inline void wc_store_fence(void) { _mm_sfence(); }
-#elif defined(__aarch64__)
+#elif defined(__aarch64__) || defined(__riscv)
 #ifdef __cplusplus
 #include <atomic>
 static inline void wc_store_fence(void) { std::atomic_thread_fence(std::memory_order_release); }