Where can the C++11/14/17 support for specific libstdc++ releases be found?

I recently lost several hours of work because of the fact that the libstdc++ version bundled with GCC 4.8 contained an incomplete C++11 <regex> implementation. I'd like to be able to know about missing stdlib features before running into problems like this.

I assumed that because GCC 4.8 supported nearly all of the C++11 lanugage features it also implemented all of the C++11 standard library features.

Where can I check which C++11/14/17 standard library features are available in each libstdc++ release that correspond to GCC releases? The libstdc++ status page appears to only the feature list from the latest release of libstdc++.