If the beginning of the loop was also the entry block
of the function, branches were inserted to the entry block
which isn't allowed. If this occurs, create a new dummy
function entry block that branches to the start of the loop.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195493 91177308-0d34-0410-b5e6-96231b3b80d8
