add lack dependency to zlib

Author: JunyiLiu1994

cmake/external/protobuf.cmake

@@ -54,6 +54,7 @@ ExternalProject_Add(
   CONFIGURE_COMMAND
     ${CMAKE_COMMAND} ${PROTOBUF_SOURCES_DIR}/src/protobuf/cmake
     -Dprotobuf_BUILD_TESTS=OFF
+    -DZLIB_ROOT:FILEPATH=${ZLIB_ROOT}
     -DCMAKE_POSITION_INDEPENDENT_CODE=ON
     -DCMAKE_BUILD_TYPE=Release
     -DCMAKE_INSTALL_PREFIX=${PROTOBUF_INSTALL_DIR}