Provide -ld_new linker build flag for the macOS build.

[corona10]

From Xcode15, apple provides a new linker(, which is faster than the classic linker.
(But from my analysis, it is up to workload..)
See: https://news.ycombinator.com/item?id=36218330

It would be great if the CPython is built on Xcode15 and we should compare the build speed with the classic linker too.
Only thing we have to do is check installed XCode version and than set the linker to use ld_new. (old one is ld_classic) and not sure of the advantage of applying to CPython. (Because of my benchmark result was not that great for the normal build and PGO+LTO build) but for the more fat build like python-build-standalone, maybe worth to do it?

cc @ronaldoussoren @ned-deily @zanieb

[ned-deily]

I believe that the new linker is the default as of Xcode 15 and the classic linker is only used if explicitly requested and produces a deprecation warning if selected with the current Xcode 16. So there shouldn't be anything that we need to do to use the new linker as of Xcode 15. That said, there are some new features that we might want to investigate using, like Mergeable Libraries, but that's a separate matter.

[corona10]

Yeah in that case we could close this issue. Thabk you for checking the fact!