We shifted the MachineBasicBlocks to the end of the MachineFunction in
DFS order. This will not ensure that MachineBasicBlocks which fell
through to one another will remain contiguous. Instead, implement
a stable sort algorithm for iplist.
This partially reverts commit r214150.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247978 91177308-0d34-0410-b5e6-96231b3b80d8