[llvm] Enable libc++ hardening mode for LLVM_ENABLE_ASSERTIONS (PR #130243)

[Brian Cain via llvm-commits]

androm3da wrote:

Is there a way for me to summon more buildbots to test this change pre-commit?  Or is there an index somewhere which would tell me which of them uses `LLVM_ENABLE_LIBCXX`?

https://github.com/llvm/llvm-project/pull/130243