[llvm] [CMake] Re-add -fno-rtti to llvm-config --cxxflags (PR #174084)

[Alexis Engelke via llvm-commits]

aengelke wrote:

Is this reproducible with a clean cmake configuration? Is LLVM_OPTIMIZED_TABLEGEN set or is this a cross compilation? Can you share the cmake configuration and the compilation commands that lead to the error?

https://github.com/llvm/llvm-project/pull/174084