[clang] Fix incorrect call to TextDiagnostic::printDiagnosticMessage

As per the documentation, the 2nd argument in printDiagnosticMessage
should be a bool that specifies whether the underlying message is a
continuation note diagnostic or not. More specifically, it should be:
```
Level == DiagnosticsEngine::Note
```
instead of:
```
Level
```

This change means that `no input file` in the following scenario will be
now correctly printed in bold:
```
$ bin/clang
clang: error: no input files
```
In terminals that don't support text formatting the behaviour doesn't
change.

Differential Revision: https://reviews.llvm.org/D87816

clang/lib/Frontend/TextDiagnosticPrinter.cpp

@@ -135,10 +135,10 @@ void TextDiagnosticPrinter::HandleDiagnostic(DiagnosticsEngine::Level Level,
   if (!Info.getLocation().isValid()) {
     TextDiagnostic::printDiagnosticLevel(OS, Level, DiagOpts->ShowColors,
                                          DiagOpts->CLFallbackMode);
-    TextDiagnostic::printDiagnosticMessage(OS, Level, DiagMessageStream.str(),
-                                           OS.tell() - StartOfLocationInfo,
-                                           DiagOpts->MessageLength,
-                                           DiagOpts->ShowColors);
+    TextDiagnostic::printDiagnosticMessage(
+        OS, /*IsSupplemental=*/Level == DiagnosticsEngine::Note,
+        DiagMessageStream.str(), OS.tell() - StartOfLocationInfo,
+        DiagOpts->MessageLength, DiagOpts->ShowColors);
     OS.flush();
     return;
   }