Add linking libatomic command to build.rs to allow building for riscv…

…64gc-unknown-linux-gnu target (#875)

librocksdb-sys/build.rs

@@ -252,7 +252,10 @@ fn build_rocksdb() {
         config.flag("-Wno-strict-aliasing");
         config.flag("-Wno-invalid-offsetof");
     }
-
+    if target.contains("riscv64gc") {
+        // link libatomic required to build for riscv64gc
+        println!("cargo:rustc-link-lib=atomic");
+    }
     for file in lib_sources {
         config.file(format!("rocksdb/{file}"));
     }