[MergeICmps] Adapt to non-eq comparisons, bugfix

Fix the last runtime issue as some sequent comparisons need be spilted.
For the origin equal comparisons chain, the new spilted Icmp chain will
still be end with equal, while for the new not-equal comparisons chain,
the new spilted Icmp chain will still be end with equal, so should address
this carefully, see detail wih case partial_sequent_ne

Thanks for @aeubanks, @glandium and @ayzhao report the runtime issue
and carefully examine.
Fix https://github.com/llvm/llvm-project/issues/59740.

Reviewed By: vitalybuka
Differential Revision: https://reviews.llvm.org/D141188