Recent builds of libcxx actually wrap an std::map's children values in a union...

Recent builds of libcxx actually wrap an std::map's children values in a union containing either a member named __cc, or either of __cc and __nc (const vs. non-const). This level of wrapping is quite useless for LLDB to show to people, so try to detect it, and filter it out

llvm-svn: 217651