[llvm] [PowerPC] fix lowering of SPILL_CRBIT on pwr9 and pwr10 (PR #146424)

[Amy Kwan via llvm-commits]

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@@ -1102,13 +1102,20 @@ void PPCRegisterInfo::lowerCRBitSpilling(MachineBasicBlock::iterator II,
     SpillsKnownBit = true;
     break;
   default:
+    // When spilling a CR bit, The super register may not be explicitly defined
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amy-kwan wrote:

```suggestion
    // When spilling a CR bit, the super register may not be explicitly defined
```
Minor nit on the comment.

https://github.com/llvm/llvm-project/pull/146424