[llvm] [CodeGen] Restore MachineBlockPlacement block ordering (PR #99351)

[William Junda Huang via llvm-commits]

huangjd wrote:

Actually a way to keep the blocks in BlockFilterSet same order as in Function is to number them. I am about to propose an RFC that adds a custom data field to BasicBlock because there are multiple other use cases that can benefit from that. This is also much more efficient than mapping BB to number. 

If this is not urgent is it ok to wait for the RFC?

https://github.com/llvm/llvm-project/pull/99351