implemented on top of a functional AVL tree. The AVL balancing code
is inspired by the OCaml implementation of Map, which also uses a functional
AVL tree.
Documentation is currently limited and cleanups are planned, but this code
compiles and has been tested.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42813 91177308-0d34-0410-b5e6-96231b3b80d8