[R-package] fix DllExport
[R-package] fix DllExport

huanzhang12/lightgbm-gpu,sightmachine/LightGBM,Allardvm/LightGBM,fstonezst/LightGBM,Laurae2/LightGBM,olofer/LightGBM,huanzhang12/LightGBM,olofer/LightGBM,wxchan/LightGBM,huanzhang12/LightGBM,Laurae2/LightGBM,henry0312/LightGBM,Allardvm/LightGBM,Laurae2/LightGBM,huanzhang12/lightgbm-gpu,cbecker/LightGBM,fstonezst/LightGBM,microsoft/LightGBM,olofer/LightGBM,fstonezst/LightGBM,wxchan/LightGBM,henry0312/LightGBM,huanzhang12/lightgbm-gpu,huanzhang12/lightgbm-gpu,cbecker/LightGBM,Allardvm/LightGBM,Laurae2/LightGBM,wxchan/LightGBM,cbecker/LightGBM,sightmachine/LightGBM,microsoft/LightGBM,fstonezst/LightGBM,cbecker/LightGBM,microsoft/LightGBM,olofer/LightGBM,olofer/LightGBM,Laurae2/LightGBM,wxchan/LightGBM,microsoft/LightGBM,huanzhang12/LightGBM,Allardvm/LightGBM,henry0312/LightGBM,microsoft/LightGBM,huanzhang12/lightgbm-gpu,fstonezst/LightGBM,Allardvm/LightGBM,sightmachine/LightGBM,henry0312/LightGBM,sightmachine/LightGBM,huanzhang12/LightGBM,henry0312/LightGBM,huanzhang12/LightGBM,wxchan/LightGBM