[llvm] [ExceptionDemo] Correct and update example ExceptionDemo (PR #69485)

[Kamlesh Kumar via llvm-commits]

kamleshbhalui wrote:

@epitavy , Have you tested locally with below command?
`cmake ../llvm  -DCMAKE_BUILD_TYPE=Debug  -DLLVM_ENABLE_EH=ON -DLLVM_ENABLE_RTTI=ON -DLLVM_BUILD_EXAMPLES=ON`

https://github.com/llvm/llvm-project/pull/69485