[llvm] [AArch64] Add Apple assembly syntax for recent instructions (PR #152111)

[Peter Smith via llvm-commits]

https://github.com/smithp35 approved this pull request.

LGTM. The addition of the alternative syntax in AsmString with | matches the Base class alternative that the let is overriding.

One small annoyance is that when llvm-objdump disassembles the instruction the sdot4.s is on a tab boundary so the registers don't line up with the instructions with the longer opcodes. However I don't think that there is anything we can do about that.
```
       0: 4e9294d3      sdot.4s v19, v6, v18
       4: 4e32ecd3      fmlal.4s        v19, v6, v18
```


https://github.com/llvm/llvm-project/pull/152111