The configuration for compiling shared objects using R CMD SHLIB
are set in file Makeconf. To change how the C++ code is
compiled, modify this file. For RStan, package inline
compiles the C++ code using R CMD SHLIB. To speed up compiled
Stan models, increase the optimization level to -O3 defined
in property CXXFLAGS in the file Makeconf.
This file may also be modified to specify alternative C++ compilers,
such as clang++ or later versions of g++.