[clang] [llvm] [LLVM][AArch64] Add ASM constraints for reduced GPR register ranges. (PR #70970)

[Peter Waller via cfe-commits]

peterwaller-arm wrote:

Worth a simultaneous update to the langref?

https://github.com/llvm/llvm-project/blob/e2564b27472638d2e2019e6cd2fc6d6d608f8b8c/llvm/docs/LangRef.rst#L5080-L5106

https://github.com/llvm/llvm-project/pull/70970