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

[Ellis Hoag via llvm-commits]

ellishg wrote:

> However, this should probably not be changed between different runs of LLD

What do you mean by this? Why not create a new LLD flag? Maybe `-thunk-scale` or `-slop-scale`?

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