[llvm] [InstCombine] Emit fatal error on void to non-void conversion (PR #96574)

[via llvm-commits]

yozhu wrote:

If this shows up in one translation unit, clang will report error and stop compilation. Would it make sense if we also abort the compilation when this is seen at LTO in link time (when the declaration and reference of callee is from one translation unit and the definition of callee is from another translation unit)? For one of our applications, this results in random / non-deterministic behaviors at runtime in "benign" case, and in worst case this causes app crash.

https://github.com/llvm/llvm-project/pull/96574