[llvm] [FuzzMutate] Reject invalid inputs in the IR fuzzers (PR #202348)

[Manuel Carrasco via llvm-commits]

mgcarrasco wrote:

I see that ignoring broken inputs can be useful, but also depending on the objective allowing invalid inputs is not necessarily wrong. Invalid inputs can still find crashes in the parser or verifier.

Would it be possible to put this change behind a flag?

https://github.com/llvm/llvm-project/pull/202348