Use CFG connectedness as a secondary sort key when deciding the order of copy coalescing.

Use CFG connectedness as a secondary sort key when deciding the order of copy coalescing.

This means that well connected blocks are copy coalesced before the less connected blocks. Connected blocks are more difficult to
coalesce because intervals are more complicated, so handling them first gives a greater chance of success.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90194 91177308-0d34-0410-b5e6-96231b3b80d8