[R] false-positive warning on CRAN

[jameslamb]

I was looking at https://cran.r-project.org/web/checks/check_results_xgboost.html tonight (looking for evidence of something while dealing with microsoft/LightGBM#3338 (comment)) and I saw that {xgboost} has a WARNING on Mac

I think this is just because R CMD check counts WARNINGs by literally grepping for the string "WARNING". This could be fixed by removing the word "WARNING" from this message:

xgboost/R-package/configure.ac

Line 42 in e033caa

echo 'WARNING: OpenMP is unavailable on this Mac OSX system. Training speed may be suboptimal.'

I'd be happy to open a PR that does that if you're interested!

[hcho3]

@jameslamb Nice catch! Yes, a pull request is welcome. I will review it.