title: Warning message: 'c:/Rtools/mingw_/bin/g++' not found
body: <p>When I try to use RStan (which needs RTools to run) in R, I get the following warning message:</p>
  <blockquote>
  <p>Warning message: In system(paste(CXX, ARGS), ignore.stdout = TRUE,
  ignore.stderr = TRUE) :   'c:/Rtools/mingw_/bin/g++' not found</p>
  </blockquote>
  <p>But, when I check in the 'c:/Rtools/' folder, I find two 'mingw_' files, called 'mingw_32' and 'min_gw64', and in both folders there is already a 'bin/g++' file. Why do I get this warning then? Is it wrong to have two folders, one 32 and one 64 bits?</p>