[libcxx] [libcxxabi] [llvm] [libc++][hardening] Introduce assertion semantics. (PR #149459)

[Konstantin Varlamov via llvm-commits]

var-const wrote:

Merging now -- the only CI failure is an unrelated infrastructure issue (`Build Docker images for libc++ CI / build-and-push`).

https://github.com/llvm/llvm-project/pull/149459