LLVM has their own ARMv8/AArch64 backend that is unrelated to Apple's. This backend, as far as I understand, does not target Apple's modified conventions and file formats for iOS. A patch was provided for this, and as far as I understand it was not merged. The patch was ignored on the mailing list, and even came with the caveat attached "I'm not sure if the llvm maintainers want the patch given the previous message that there's going to be an official patch set from apple to support this, but here is mine."

http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-September/06...

For further evidence of this, we can look to Haskell: Haskell currently has been unable to target iOS's ARM64 architecture because of this part of the compiler not being open source. It is precisely these kinds of ripple effects that Stallman is concerned with: he would argue that by supporting LLVM the community set themselves up for a situation where Apple was able to later hoard valuable changes while still getting the benefit of an army of people fixing bugs in their compiler for free.

> Also in "Build Settings", change "Architectures" to "Standard Architectures (armv7, armv7s)" (as opposed to "(including 64-bit)") as Apple hasn't yet merged Arm64 support into the LLVM source that we'd need to fully support 64bit iOS devices. The code will still run wonderfully on the 5S/iPad Air/mini Retina in 32bit mode.

https://ghc.haskell.org/trac/ghc/wiki/Building/CrossCompilin...

Honestly, it is as if you just saw "ARM64", did a Google search, took the first hit, and decided "that's enough research for today"... :(. Your citation is from over a year ago, long before all of this happened, and is not relevant. I specifically stated in my comment that the issue was with relation to the "ARM64" backend as it targets "iOS", not the general "AArch64" backend as it could be used to target other platforms or operating systems. This is a critical distinction when talking about Apple.