In DwarfEHPrepare, after all passes are run, RewindFunction may be a dangling
pointer to a dead function. To make sure it's valid, doFinalization nullptrs
RewindFunction just like the constructor and so it will be found on next run.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217737 91177308-0d34-0410-b5e6-96231b3b80d8