make MockTimeEnv::current_time_ atomic to fix data race

Summary:
fix a new TSAN failure
https://gist.github.com/miasantreble/7599c33f4e17da1024c67d4540dbe397
Closes https://github.com/facebook/rocksdb/pull/3694

Differential Revision: D7565310

Pulled By: miasantreble

fbshipit-source-id: f672c96e925797b34dec6e20b59527e8eebaa825

db/db_test_util.h

@@ -606,7 +606,7 @@ class MockTimeEnv : public EnvWrapper {
   }
 
  private:
-  uint64_t current_time_ = 0;
+  std::atomic<uint64_t> current_time_{0};
 };
 
 #ifndef ROCKSDB_LITE

util/status.cc

@@ -19,6 +19,7 @@ const char* Status::CopyState(const char* state) {
       std::strlen(state) + 1; // +1 for the null terminator
   char* const result =
       new char[cch];
+  result[cch - 1] = '\0';
 #ifdef OS_WIN
   errno_t ret;
   ret = strncpy_s(result, cch, state, cch - 1);