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

[Louis Dionne via llvm-commits]

ldionne wrote:

> I would much rather we do what our users tend to do here, and that's build with rtti enabled, and then disable rtti only during the test suite run.

In reality, we have instances of both things happening. Most embedded configurations will actually build the library without RTTI. I wonder if we really want to test both combinations -- we generally don't.

I do agree that most users on e.g. desktops will disable RTTI yet their dylib will have been built with RTTI enabled. I think there's a question of how we want to approach this configuration explosion. FWIW I could even be talked into dropping support for building the library without RTTI -- I wonder how much impact this actually has on the size of the library but I suspect not that much.

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