[llvm] Add -Wms-bitfield-padding warning when possible (PR #139828)

[Oliver Hunt via llvm-commits]

ojhunt wrote:

> > > > @mstorsjo @Endilll @IanWood1 given you're doing stage2+ builds would you folk mind seeing if this warning triggers for you? after applying #139825 if possible
> > > 
> > > 
> > > I applied changes from both PRs, and I'm seeing the following warnings (heavily deduplicated):
> > 
> > 
> > Thank you very much! I'll try to add the fixes for those ones.
> > What targets do you have enabled?
> 
> Only X86

would you mind checking now that https://github.com/llvm/llvm-project/pull/139825 has been merged?

https://github.com/llvm/llvm-project/pull/139828