Worth noting that libstdc++, whilst a separate project, is not yet feature complete.
http://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html#s...
http://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html#s...
> libc++ is a 100% complete C++11 implementation on Apple's OS X.
Clang definitely lets you easily switch between libstdc++ and libc++.
Maybe they've fixed this by now, I dunno. [Though the wording in that blurb, "100% complete C++11 implementation on Apple's OS X" doesn't inspire confidence...]