Follow up with linker related comments from #19240:
Actually, after digging through @fanquake's recommendation some more, it looks like the LD64_VERSION_NUM does not end up being passed through correctly. .... I suggest we take theuni@7181800 as part of this PR as well. Then maybe we can send @fanquake down the rabbit hole to see why clang can't find this on its own (or if it's even supposed to).