Unintuitive and all as it looks, it's actually okay, on 10.9 g++ is not actually GCC, it is clang:
`$ g++ --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 5.0 (clang-500.2.79) (based on LLVM 3.3svn)
Target: x86_64-apple-darwin13.1.0
Thread model: posix`
But g++ -dumpversion still returns something sensible, and the project still builds.