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

[Dimitry Andric via llvm-commits]

DimitryAndric wrote:

There is no particular reason, except that this is the configuration you get when building FreeBSD with `WITHOUT_LLVM_ASSERTIONS` enabled. We are using a few pre-generated header files, which set `LLVM_ENABLE_ABI_BREAKING_CHECKS=1`, but I was not aware that this define is coupled to `NDEBUG`. If that is the case, there should really only be checks for `LLVM_ENABLE_ABI_BREAKING_CHECKS`?

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