Update build_r.R (#1918)
Update build_r.R (#1918)

add boost header files compute/ into build_r.R to enable GPU compilation
henry0312/LightGBM,microsoft/LightGBM,microsoft/LightGBM,microsoft/LightGBM,henry0312/LightGBM,henry0312/LightGBM,henry0312/LightGBM,henry0312/LightGBM,microsoft/LightGBM,microsoft/LightGBM