[MSVC] RocksDB failed to build with msvc due to warning C4189 on Windows

[Zhaojun-Liu]

Hi, Recently, we updated the commit of RocksDB (commit is: 76de3c8), it failed to build with msvc due to the warning C4189 like below, could you help look this issue? Thanks.

F:\gitP\facebook\rocksdb\db\c_test.c(281,10): warning C4189: 'cf_size': local variable is initialized but not referenced [F:\gitP\facebook\rocksdb\build_amd64\c_test.vcxproj]
         F:\gitP\facebook\rocksdb\db\c_test.c(283,10): warning C4189: 'cf_file_count': local variable is initialized but not referenced [F:\gitP\facebook\rocksdb\build_amd64\c_test.vcxproj]

Expected behavior

build successfully.

Actual behavior

"F:\gitP\facebook\rocksdb\build_amd64\rocksdb.sln" (Rebuild target) (1) ->
       "F:\gitP\facebook\rocksdb\build_amd64\c_test.vcxproj.metaproj" (Rebuild target) (5) ->
       "F:\gitP\facebook\rocksdb\build_amd64\c_test.vcxproj" (Rebuild target) (46) ->
       (ClCompile target) -> 
         F:\gitP\facebook\rocksdb\db\c_test.c(281,10): warning C4189: 'cf_size': local variable is initialized but not referenced [F:\gitP\facebook\rocksdb\build_amd64\c_test.vcxproj]
         F:\gitP\facebook\rocksdb\db\c_test.c(283,10): warning C4189: 'cf_file_count': local variable is initialized but not referenced [F:\gitP\facebook\rocksdb\build_amd64\c_test.vcxproj]


       "F:\gitP\facebook\rocksdb\build_amd64\rocksdb.sln" (Rebuild target) (1) ->
       "F:\gitP\facebook\rocksdb\build_amd64\c_test.vcxproj.metaproj" (Rebuild target) (5) ->
       "F:\gitP\facebook\rocksdb\build_amd64\c_test.vcxproj" (Rebuild target) (46) ->
       (ClCompile target) -> 
         F:\gitP\facebook\rocksdb\db\c_test.c(281,10): error C2220: the following warning is treated as an error [F:\gitP\facebook\rocksdb\build_amd64\c_test.vcxproj]

    2 Warning(s)
    1 Error(s)

Steps to reproduce the behavior

1. git clone https://github.com/facebook/rocksdb F:\gitP\facebook\rocksdb
2. Open VS2019 x64 Native tools command prompt
3. mkdir F:\gitP\facebook\rocksdb\build_amd64 && cd F:\gitP\facebook\rocksdb\build_amd64
4. cmake -G "Visual Studio 16 2019" -A x64 -DCMAKE_SYSTEM_VERSION=10.0.18362.0 .. 2>&1
5. msbuild /m /p:Platform=x64 /p:Configuration=Release rocksdb.sln /t:Rebuild /p:BuildInParallel=true 2>&1

More info: VS version: VS16.11.18 OS: Windows server 2019

detailed log: build (4).log