[llvm] Add __attribute__((warn_unused_result)) to LLVMErrorRef (PR #87025)

[David Blaikie via llvm-commits]

dwblaikie wrote:

@AaronBallman updated this from the phab review to use your suggested `LLVM_NODISCARD_TYPEDEF`  naming. Though my own comment that we probably need a narrower clang version check ( https://reviews.llvm.org/D153163#inline-1484444 ) is still outstanding.

If folks have ideas on that, otherwise I'll try to throw something together to address that as best I can soon.

https://github.com/llvm/llvm-project/pull/87025