Clean up the AST for while loops and fix several problems with

Clean up the AST for while loops and fix several problems with
cleanups for while loops:

1) Make sure that we destroy the condition variable of a while statement each time through the loop for, e.g.,

   while (shared_ptr<WorkInt> p = getWorkItem()) {
         // ...
         }

2) Make sure that we always enter a new cleanup scope for the body of the while loop, even when there is no compound expression, e.g.,

   while (blah)
     RAIIObject raii(blah+1);

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@89800 91177308-0d34-0410-b5e6-96231b3b80d8