C++11 on Snow Leopard 10.6.8
The process to install c++11 on 10.6.8 on MacPorts has recently been automated, and for the majority of users, now happens automatically. The previous instructions you were following are no longer necessary.

The installation process leads to MacOSX 10.6.8 running with a reasonably current libc++, clang-8.0 (at present -- clang-9.0 is available as well), and the required underpinnings in cctools (assembler, ranlib, etc) and ld64 (linker) to install software requiring the currently available c++17 standards, and newer as clang/llvm progress.