Fix build issue when protobuf is installed in system

CMakeLists.txt

@@ -40,8 +40,12 @@ if(WIN32)
     set(PROTOBUF_LIBRARIES_PATH ${PROTOBUF_INSTALATION_PATH}/lib)
     target_link_libraries(${PROJECT_NAME} "${PROTOBUF_LIBRARIES_PATH}/libprotobuf.lib")
     target_link_libraries(${PROJECT_NAME} "${PROTOBUF_LIBRARIES_PATH}/libprotoc.lib")
-elseif (UNIX)
-    target_link_libraries(${PROJECT_NAME} libprotoc)
+elseif(UNIX)
+    if(NOT Protobuf_FOUND)
+        target_link_libraries(${PROJECT_NAME} libprotoc)
+    else()
+        target_link_libraries(${PROJECT_NAME} ${Protobuf_LIBRARIES} -lprotoc)
+    endif()
 endif()
 
 add_subdirectory("src/lib")