[libcxx] Fix for ALL undefined behavior in <list>.
This patch fixes std::list for builtin pointer types in the current ABI version and fixes std::list for all fancy pointer types in the next ABI version. The patch was designed to minimize the amount of code needed to support both ABI configurations. Currently only ~5 lines of code differ.
Reviewers: danalbert, jroelofs, mclow.lists
Subscribers: dexonsmith, awi, cfe-commits
Differential Revision: http://reviews.llvm.org/D12299