[llvm] [llvm-exegesis] Add explicit support for setting DF in X86 (PR #115644)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

> Hm wait, actually only DF is required to be cleared, sorry for the noise.

Right. `df` isn't in there either, but I think that might just be an oversight.

Either way, something that I plan on addressing in a future patch to keep things focused, given this already occurs when setting `eflags` ourselves.

https://github.com/llvm/llvm-project/pull/115644