Summary:
* added missing override specifiers for overriden methods
this fixes compiler warnings emitted by g++ and clang++ when compile option `-Wsuggest-override` is turned on.
* fix compile warning with -Wmaybe-uninitialized
g++-11 warns about a _potentially_ uninitialized variable when using `-Wmaybe_uninitialized`:
```
env/env.cc: In member function ‘virtual rocksdb::Status rocksdb::Env::GetHostNameString(std::string*)’:
env/env.cc:738:66: error: ‘hostname_buf’ may be used uninitialized [-Werror=maybe-uninitialized]
738 | Status s = GetHostName(hostname_buf.data(), hostname_buf.size());
| ^
In file included from /usr/include/c++/11/tuple:39,
from /usr/include/c++/11/functional:54,
from ./include/rocksdb/env.h:22,
from env/env.cc:10:
/usr/include/c++/11/array:176:7: note: by argument 1 of type ‘const std::array<char, 256>*’ to ‘constexpr std::array<_Tp, _Nm>::size_type std::array<_Tp, _Nm>::size() const [with _Tp = char; long unsigned int _Nm = 256]’ declared here
176 | size() const noexcept { return _Nm; }
| ^~~~
env/env.cc:737:37: note: ‘hostname_buf’ declared here
737 | std::array<char, kMaxHostNameLen> hostname_buf;
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9199
Reviewed By: jay-zhuang
Differential Revision: D32630703
Pulled By: pdillinger
fbshipit-source-id: 9ea3010b1105a582548e3c3c0db4475b201e4a10
5384f0af6e