[clang][preprocessor] Allow calling DumpToken() on annotation tokens

[tbaeder]

Summary

The getSpelling() call otherwise ultimately runs into an assertion because getLength() is called on an annotation token.

Just ran into this when debugging using -dump-tokens.
Sorry I can't really find a better reviewer, the rest of that function seems to be pretty ancient.

[aaron.ballman]

LGTM! I don't think there's a particularly strong need to add test coverage for this as the dump method is a debugging aid.

clang/lib/Lex/Preprocessor.cpp

 
 void Preprocessor::FinalizeForModelFile() {
   NumEnteredSourceFiles = 1;
 
   PragmaHandlers = std::move(PragmaHandlersBackup);
 }
 
 void Preprocessor::DumpToken(const Token &Tok, bool DumpFlags) const {
-  llvm::errs() << tok::getTokenName(Tok.getKind()) << " '"
-               << getSpelling(Tok) << "'";
+  llvm::errs() << tok::getTokenName(Tok.getKind());
+
+  if (!Tok.isAnnotation())
+    llvm::errs() << " '" << getSpelling(Tok) << "'";
 
   if (!DumpFlags) return;
 
   llvm::errs() << "\t";
   if (Tok.isAtStartOfLine())
     llvm::errs() << " [StartOfLine]";
   if (Tok.hasLeadingSpace())
     llvm::errs() << " [LeadingSpace]";