[clang] [clang-tools-extra] [llvm] [Clang] Fix : More Detailed "No expected directives found" (PR #78338)

[Aaron Ballman via cfe-commits]

================
@@ -396,6 +396,15 @@ class VerifyDiagnosticConsumer::MarkerTracker {
   }
 };
 
+std::string DetailedErrorString(DiagnosticsEngine &Diags) {
+  std::string ErrDirective;
+  if (Diags.getDiagnosticOptions().VerifyPrefixes.empty())
+    ErrDirective = "expected";
+  else
+    ErrDirective = *Diags.getDiagnosticOptions().VerifyPrefixes.begin();
+  return ErrDirective;
+}
----------------
AaronBallman wrote:

```suggestion
static std::string DetailedErrorString(const DiagnosticsEngine &Diags) {
  if (Diags.getDiagnosticOptions().VerifyPrefixes.empty())
    return "expected";
  return *Diags.getDiagnosticOptions().VerifyPrefixes.begin();
}
```
Some minor changes here but are mostly NFC.

https://github.com/llvm/llvm-project/pull/78338