[llvm] [DAGCombiner] Ensure poison-generating flags are stripped in `freeze` op (PR #114582)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> > When combining freeze in DAG, poison-generating flags were previously not fully removed as intended. This change explicitly drops these flags from freeze operand, ensuring a fixed, non-poisonous value at this point in computation.
> 
> Sorry if I've missed something (long day), but where was it intended that the poison flags should be removed?

I might be missing something, but if I read this correctly, the line following the comment would be supposed to strip the flags from the current node (which doesn't carry any flags), and getNode doesn't actually drop any flags. To be correct, it seems that no flags are set in FlagsInserter in the current DAG, except that `samesign` is there.

https://github.com/llvm/llvm-project/pull/114582