[llvm] [WIP][RFC] Teach MCA constant registers do not create dependencies (PR #89387)

[Rin Dobrescu via llvm-commits]

Rin18 wrote:

> > This will increase the size of generated code, which is an issue.
> 
> MCRegisterDesc is 22 bytes before this change but requires 4 byte alignment so I think the bool sneaks into the 2 byte padding.

I was not aware of that, this is reassuring. 

https://github.com/llvm/llvm-project/pull/89387