[llvm] [ConstraintElim] Drop invalid rows instead of failing the elimination (PR #76299)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> Why is it valid to simply drop these rows? Doesn't this mean we lose constraints?

`sat` means that the constraint system ***may*** have a solution. Returning `sat` for an inconsistent system is allowed. So it is safe to drop constraints.


https://github.com/llvm/llvm-project/pull/76299