Certain optimization passes (like globaldce) can prune function
declaration that SjLjEHPrepare assumed would exit when it'd
runOnFunction.
This fixes PR26669.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@261303 91177308-0d34-0410-b5e6-96231b3b80d8