[clang] [clang][bytecode] Bail out from type-punning casts (PR #163809)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

You don't have tests, which bothers me because it is not clear what you are focusing on.

Maybe we can focus on a non-crashing case like this one: https://godbolt.org/z/ccjjvPKjh

which the new interpreter accepts but the existing constexpr engine does not, correctly so. 

Then we can see if fixing these other simpler cases also fixes this as well. We do reject some reinterpret cast cases like this one: https://godbolt.org/z/cox48zoEG

So the existing code to catch that should be modified to catch the other cases.

https://github.com/llvm/llvm-project/pull/163809