Where are g++ stl libraries in Darwin
OS X does not include c++ compilers.

You need to install Xcode and/or its command line tools to get clang (note not gcc)

The C++ standard libraries (which do not need to be actual files  but are in libc++ which is the Xcode default library) The include files are in /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/