[llvm] [NFC][MC] Use `llvm_unreachable` for unreachable case (PR #152930)

[Fangrui Song via llvm-commits]

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@@ -72,7 +72,7 @@ static void emitCATTR(raw_ostream &OS, StringRef Name, GOFF::ESDRmode Rmode,
       OS << "64";
       break;
     case GOFF::ESD_RMODE_None:
-      break;
+      llvm_unreachable("GOFF::ESD_RMODE_None should not be handled here");
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MaskRay wrote:

I would move `GOFF::ESD_RMODE_None:` above to make it clear that this case has already been handled and use an empty llvm_unreachable as it's obvious.

https://github.com/llvm/llvm-project/pull/152930