[llvm] [SampleFDO] Improve stale profile matching by diff algorithm (PR #87375)

[Lei Wang via llvm-commits]

wlei-llvm wrote:

> Can we add a lit test case to verify the new diffing? something that will yield different results with new diffing algorithm.

The test change in the new version can verify the algorithm(yield different results).

the original one is 
Profile: `bar foo bar foo`
IR  :       `bar foo bar foo`
Now I remove the 1st bar in the profile, the old algorithm will match the 2nd bar to the 1st bar in the IR, but diff algorithm will keep the same match. 

Though it's simple and a bit tricky, I can add a complicated case. 



https://github.com/llvm/llvm-project/pull/87375