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

[Louis Dionne via llvm-commits]

================
@@ -374,6 +376,11 @@ if (LIBCXX_HAS_PTHREAD_API)
   endif()
 endif()
 
+if (NOT LIBCXX_ENABLE_RTTI AND LIBCXX_ENABLE_EXCEPTIONS)
+  message(FATAL_ERROR "The option LIBCXX_ENABLE_RTTI can not be turned off"
----------------
ldionne wrote:

I suggest:

```
Libc++ cannot be built with exceptions enabled but RTTI disabled, since that configuration is broken. See [#66117](https://github.com/llvm/llvm-project/issues/66117) for details.
```

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