[clang] [clang][Sema] Add -Wswitch-default warning option (PR #73077)

[Aaron Ballman via cfe-commits]

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@@ -10044,6 +10044,8 @@ def warn_missing_case : Warning<"%plural{"
   "3:enumeration values %1, %2, and %3 not handled in switch|"
   ":%0 enumeration values not handled in switch: %1, %2, %3...}0">,
   InGroup<Switch>;
+def warn_switch_default : Warning<"switch missing default case">,
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AaronBallman wrote:

```suggestion
def warn_switch_default : Warning<"'switch' missing 'default' label">,
```

https://github.com/llvm/llvm-project/pull/73077