[Fix](compile) Fix gcc compile on master (#33864)

This is imported by #33511. wrongly used

ColumnStr<T> ();

which violate C++20 standard(see https://wg21.cmeerw.net/cwg/issue2237) but still supported by clang up until now(see llvm/llvm-project#58112)

be/src/runtime/snapshot_loader.cpp

@@ -778,6 +778,7 @@ Status SnapshotLoader::move(const std::string& snapshot_path, TabletSharedPtr ta
 
     } else {
         LOG(FATAL) << "only support overwrite now";
+        __builtin_unreachable();
     }
 
     // snapshot loader not need to change tablet uid