Adding a custom summary for libc++ std::vector<bool>
vector<bool> is specialized and the existing general summary for vectors would lie to the user.
Tackling libstdc++ and synthetic children is the following, less critical, part of this task



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@172671 91177308-0d34-0410-b5e6-96231b3b80d8