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

[Scott Todd via llvm-commits]

ScottTodd wrote:

We do jump through some hoops with asserts and NDEBUG downstream, yeah: https://github.com/iree-org/iree/blob/ff1b8b0e433372b73ad6abcaa101ae0dc2fd639d/CMakeLists.txt#L477-L522. I'm seeing if I can find better upstream repro steps...

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