New category "gnu-libstdc++" provides summary for std::string and synthetic...

New category "gnu-libstdc++" provides summary for std::string and synthetic children for types std::map, std::list and std::vector
 The category is enabled by default. If you run into issues with it, disable it and the previous behavior of LLDB is restored
 ** This is a temporary solution. The general solution to having formatters pulled in at startup should involve going through the Platform.
Fixed an issue in type synthetic list where a category with synthetic providers in it was not shown if all the providers were regex-based

llvm-svn: 137850