[llvm] [libcxx] [libc++][CI] Tests the no RTTI configuration. (PR #65518)

[Mark de Wever via llvm-commits]

mordante wrote:

The reason for adding the configuration is that users can do this and it was not tested.

Maybe we should brainstorm how we can avoid running all configurations for all patches, but still allow to run them manually. For example, format related patches really should test no-wide-characters, mdspan patches are very unlikely to find an issue in that configuration.

https://github.com/llvm/llvm-project/pull/65518