by default boost has build with cxx11 support on mac 10.13 high sierra with xcode 9.4
to avoid link errors with c++14,it should build with c++14 support
./b2 link=static cxxflags="-std=c++14" -d+2 stage
// ./b2 .....
//on gentoo may has error: "none" is not a known value of feature
//this because boost installed and the file /usr/share/boost-build/site-config.jam