libstdc++ deprecation warning

When I build using libstdc++ on a Mac, I get a warning:

clang: warning: libstdc++ is deprecated; move to libc++ with a minimum deployment target of OS X 10.9 [-Wdeprecated]

I'm just wondering, why does it specify a deployment target of 10.9? As far as I know, libc++ should be able to go back to 10.7.

Hi James,