that it doesn't have dangling pointers when abstract types are resolved. This
modifies it somewhat to address comments: making the "StructLayoutMap" an
anonymous structure, calling "removeAbstractTypeUser" when appropriate, and
adding asserts where helpful.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90362 91177308-0d34-0410-b5e6-96231b3b80d8