[llvm] Reserve R9 on armv6 iOS 2.x (PR #150835)

[via llvm-commits]

Un1q32 wrote:

> I haven't done the "archaeology" to check this, but it seems fine: IIUC the worst case fallout is that this hurts performance on a no-longer-supported platform, and best case is that it fixes this bug... so the tradeoff seems fine in light of that.

I actually have the hardware to test with, and I've been carrying this patch for a while in my personal clang builds.  Without it anything non-trivial segfaults, and with it everything works. I can probably find where this is done in the old Apple GCC sources and link that here.

https://github.com/llvm/llvm-project/pull/150835