[llvm] [ADT] Fix ArrayRef<T>::slice (PR #113048)

[via llvm-commits]

FLZ101 wrote:

> Could you update the PR description and explain what the issue is?

`slice(N, size() - N)` will never fail the assertion `assert(N+M <= size() && "Invalid specifier")` above, even `N > size()`.

https://github.com/llvm/llvm-project/pull/113048