[lld] [lld-macho]Define a macro to allow specifying the slop size at build time. (PR #164295)

[Peter Rong via llvm-commits]

DataCorrupted wrote:

@ellishg  I think what he meant is that for a given lld (binary executable), it should produce the same result; if you want something different, build a separate lld. But I agree with you: I don't see the motivation in this; a flag would be better IMO

https://github.com/llvm/llvm-project/pull/164295