[libcxxabi] [llvm] [libcxxabi] Fix PODSmallVector zero-capacity growth (PR #215386)

[Nikolas Klauser via llvm-commits]

https://github.com/philnik777 requested changes to this pull request.

Can we just `static_assert` that `N > 0` instead?

https://github.com/llvm/llvm-project/pull/215386