[llvm] [FuzzMutate] Prevent the mutator from generating illegal memory operations (PR #144885)

[Manuel Carrasco via llvm-commits]

mgcarrasco wrote:

@DataCorrupted thanks again for the feedback. I've added a unit test. We ae also planning to incorporate this check into the Verifier in an independent PR. Once that is done, I can also remove the adhoc check for addrspace 8. 

https://github.com/llvm/llvm-project/pull/144885