[llvm] X86: Mark flag clobbers dead in stack probe expansion (PR #227682)

[Reid Kleckner via llvm-commits]

rnk wrote:

`setOperandDead(MagicNumber)` is not the most readable. What would a decent "eflags dead" abstraction look like? Something in TII? That's where we put abstractions like `AnalyzeBranch`, right? The catch is it would break the fluent MI builder style, because eflags is such an x86-specific concept.

I guess what I'm saying is, the better the abstraction is, the more worth it it becomes.

https://github.com/llvm/llvm-project/pull/227682