try fixing protobuf build in win distribtest

test/distrib/cpp/run_distrib_test_cmake.bat

@@ -39,7 +39,7 @@ cd ../../..
 cd third_party/protobuf/cmake
 mkdir build
 cd build
-cmake -DCMAKE_INSTALL_PREFIX=%INSTALL_DIR% -Dprotobuf_MSVC_STATIC_RUNTIME=OFF -Dprotobuf_BUILD_TESTS=OFF ..
+cmake -DCMAKE_INSTALL_PREFIX=%INSTALL_DIR% -DZLIB_ROOT=%INSTALL_DIR% -Dprotobuf_MSVC_STATIC_RUNTIME=OFF -Dprotobuf_BUILD_TESTS=OFF ..
 cmake --build . --config Release --target install || goto :error
 cd ../../../..