[clang] Avoid need for SLocEntryLoaded BitVector (PR #67960)

[Giulio Eulisse via cfe-commits]

================
@@ -489,6 +490,8 @@ class SLocEntry {
 
   bool isExpansion() const { return IsExpansion; }
   bool isFile() const { return !isExpansion(); }
+  [[nodiscard]] bool isLoaded() const { return Loaded; }
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ktf wrote:

No, I guess not. It's just my clang-tidy integration being overzealous, I guess.

```suggestion
  bool isLoaded() const { return Loaded; }
```

https://github.com/llvm/llvm-project/pull/67960