[LIR][SCEVExpander] Restore original flags when aborting transform (#82362)

SCEVExpanderCleaner will currently remove instructions created by
SCEVExpander, but not restore poison generating flags that it may have
dropped. As such, running LIR can currently spuriously drop flags
without performing any transforms.

Fix this by keeping track of original instruction flags in SCEVExpander.

Fixes https://github.com/llvm/llvm-project/issues/82337.