[llvm] [mlir] Fix LLVM_ENABLE_ABI_BREAKING_CHECKS macro check: use #if instead of #ifdef (PR #110185)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

I think I can reproduce with a release build and ` -DLLVM_ABI_BREAKING_CHECKS=FORCE_ON`.

Note that this is a bit of a weird config, you may want to check your downstream settings.

https://github.com/llvm/llvm-project/pull/110185