Since the object is new'ed in the enterCFG function, now deleting in the exitCFG function instead of the destructor to ensure proper pairing. This allows reuse of the builder without creating a memory leak.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206471 91177308-0d34-0410-b5e6-96231b3b80d8