[lld] [lld-macho][NFC] Track category merger input data source language for better verification (PR #95473)

[Kyungwoo Lee via llvm-commits]

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@@ -349,11 +349,15 @@ void objc::checkCategories() {
 namespace {
 
 class ObjcCategoryMerger {
+  // In which language was a particular construct originally defined
+  enum SourceLanguage { ObjC, Swift, Unknown };
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kyulee-com wrote:

It seems natural to start with an invalid case (0) for `Unknown`.
```suggestion
  enum SourceLanguage { Unknown, ObjC, Swift };
```

https://github.com/llvm/llvm-project/pull/95473