Keep the order of the basic blocks in the cloned loop as the original

Keep the order of the basic blocks in the cloned loop as the original
loop
Summary:
Do the cloning in two steps, first allocate all the new loops, then
clone the basic blocks in the same order as the original loop.
Reviewer: Meinersbur, fhahn, kbarton, hfinkel
Reviewed By: hfinkel
Subscribers: hfinkel, hiraditya, llvm-commits
Tag: https://reviews.llvm.org/D64224
Differential Revision:

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365366 91177308-0d34-0410-b5e6-96231b3b80d8