[DeclPrinter] Handle built-in C++ types in -ast-print.

[tra]

Summary

Fixes a crash in clang when it crashed with -ast-print on code that contained decltype(nullptr).

[tra]

Never mind. There must be something else going on in the case where I've discovered the crash. the test case in this patch does not really reproduce the issue by itself. :-(

clang/lib/AST/DeclPrinter.cpp

while (!BaseType->isSpecifierType()) {
     else if (const FunctionType* FTy = BaseType->getAs<FunctionType>())
       BaseType = FTy->getReturnType();
     else if (const VectorType *VTy = BaseType->getAs<VectorType>())
       BaseType = VTy->getElementType();
     else if (const ReferenceType *RTy = BaseType->getAs<ReferenceType>())
       BaseType = RTy->getPointeeType();
     else if (const AutoType *ATy = BaseType->getAs<AutoType>())
       BaseType = ATy->getDeducedType();
+    else if (isa<BuiltinType>(BaseType))
+      break;
     else
       llvm_unreachable("Unknown declarator!");
   }
   return BaseType;
 }
 
 static QualType getDeclType(Decl* D) {
   if (TypedefNameDecl* TDD = dyn_cast<TypedefNameDecl>(D))

clang/test/Sema/ast-print-cxx.cpp

+// RUN: %clang_cc1 -std=c++11 %s -ast-print | FileCheck %s
+// RUN: %clang_cc1 -std=c++11 %s -ast-print \
+// RUN:      | %clang_cc1 -std=c++11 -x c++ -fsyntax-only -
+
+// CHECK: typedef decltype(nullptr) nullptr_t;
+typedef decltype(nullptr) nullptr_t;