[llvm] [SpeculativeExecution] Drop poison-generating flags when hoisting instructions (PR #225377)

[Adrian Kuegel via llvm-commits]

akuegel wrote:

@OCHyams @Apochens I selected you as reviewers as it seems to me that this is kind of similar to https://github.com/llvm/llvm-project/pull/97384

https://github.com/llvm/llvm-project/pull/225377