[clang] [llvm] Support the inline asm 'a' constraint on PowerPC (PR #141604)

[Kamau Bridgeman via llvm-commits]

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kamaub wrote:

```suggestion
  // The ConstraintInfo for this Operand is encoded in Op - 1 operand
```
typo

https://github.com/llvm/llvm-project/pull/141604