[clang] [CIR] Implement mustprogress/uwtable attributes (PR #228093)

[Erich Keane via cfe-commits]

erichkeane wrote:

> > > Adding this attribute also needs the trivial infinite loop handling? In classic CodeGen. CodeGenFunction::checkIfLoopMustProgress() removes the function’s mustprogress attribute when it encounters an empty loop with a constant true condition, but CIR’s emitForStmt, emitWhileStmt, and emitDoStmt currently have no equivalent handling?
> > 
> > 
> > OH! I just trusted that function was right :D Yeah, looks like i have to update that as well. Thats unfortunate...
> 
> Actually, I don't think this does? It shouldn't be a problem if we have a non-must-progress loop inside of a must-progress function. It appears that just stops the opt as well?
> 
> So it is something we could add on later, as this isn't a breaking change, right?

Oh wait, i see the loop handling removes it from the function.  Hrmph...

https://github.com/llvm/llvm-project/pull/228093