[GlobalISel] Insert translated switch icmp blocks after switch parent.

[GlobalISel] Insert translated switch icmp blocks after switch parent.

Now that we preserve the IR layout, we would end up with all the newly
synthesized switch comparison blocks at the end of the function.
Instead, use a hopefully more reasonable layout, with the comparison
blocks immediately following the switch comparison blocks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297869 91177308-0d34-0410-b5e6-96231b3b80d8