[llvm] [InstCombine] isKnownNonNegative should recognize `b - a` after `a <= b` (PR #145105)

[Ross Kirsling via llvm-commits]

rkirsling wrote:

Hmm, the bot seems to be reporting an unrelated flaky failure.

Also, mentioning @dtcxzyw since I don't have the ability to edit reviewers.

https://github.com/llvm/llvm-project/pull/145105