http://stackoverflow.com/questions/18453182/g-errors-when-trying-to-compile-c11-with-rcpp
i.e. all I did (it appears so far to work) is to create ~/.R/Makevars (the directory had to be created too) and place the following line in it:
PKG_CXXFLAGS = -std=c++11
Then the Rcpp file compiled.