Remove unnecessary default cases in switches over enums.

This allows -Wswitch-enum to find switches that need updating when these enums are modified.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@148281 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/LogDiagnosticPrinter.cpp b/lib/Frontend/LogDiagnosticPrinter.cpp
index 8b585be..8eb4673 100644
--- a/lib/Frontend/LogDiagnosticPrinter.cpp
+++ b/lib/Frontend/LogDiagnosticPrinter.cpp
@@ -12,6 +12,7 @@
 #include "clang/Basic/SourceManager.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/ErrorHandling.h"
 using namespace clang;
 
 LogDiagnosticPrinter::LogDiagnosticPrinter(raw_ostream &os,
@@ -28,14 +29,13 @@
 
 static StringRef getLevelName(DiagnosticsEngine::Level Level) {
   switch (Level) {
-  default:
-    return "<unknown>";
   case DiagnosticsEngine::Ignored: return "ignored";
   case DiagnosticsEngine::Note:    return "note";
   case DiagnosticsEngine::Warning: return "warning";
   case DiagnosticsEngine::Error:   return "error";
   case DiagnosticsEngine::Fatal:   return "fatal error";
   }
+  llvm_unreachable("Invalid DiagnosticsEngine level!");
 }
 
 // Escape XML characters inside the raw string.