[llvm] Use MapVector to fix lld thinLTO "nondeterminism" issue. (PR #117551)

[via llvm-commits]

llvmssh wrote:

> > > Probably a flake.
> > 
> > 
> > Okay, thanks for your reply. Is it necessary to confirm this?
> 
> Multiple following builds have no this error and the patch is still there. https://lab.llvm.org/buildbot/#/builders/186

Ok, thanks.

https://github.com/llvm/llvm-project/pull/117551