[lld] [lld][macho] Restructure thunk generation algorithm (PR #193367)

[Zhaoxuan Jiang via llvm-commits]

https://github.com/nocchijiang commented:

Delaying the `deferredBranchRedirects` handling until after `estimatedStubsEnd` is computed makes sense to me. These entries already have an in-range thunk fallback, but after stubs estimation we may be able to keep some of them as direct branches to `__stubs` / `__objc_stubs` instead of retargeting to the saved thunk.

https://github.com/llvm/llvm-project/pull/193367