[lldb][NFC] Refactor some IsClangType checks in ClangASTContext

[teemperor]

Summary

All type in these functions need be valid and Clang types, so
we might as well replace these checks with IsClangType.

Also lets IsClangType explicitly check for validity instead of
assuming that the TypeSystem is a nullptr.

lldb/source/Symbol/ClangASTContext.cpp

if (objc_class_type) {
         return class_interface_decl->getDefinition() != nullptr;
       return false;
     }
   }
   return true;
 }
 
 bool ClangASTContext::IsObjCClassType(const CompilerType &type) {
-  if (type) {
+  if (ClangUtil::IsClangType(type)) {
     clang::QualType qual_type(ClangUtil::GetCanonicalQualType(type));
 
     const clang::ObjCObjectPointerType *obj_pointer_type =
         llvm::dyn_cast<clang::ObjCObjectPointerType>(qual_type);
 
     if (obj_pointer_type)
       return obj_pointer_type->isObjCClassType();
   }
bool ClangASTContext::IsBeingDefined(lldb::opaque_compiler_type_t type) {
   const clang::TagType *tag_type = llvm::dyn_cast<clang::TagType>(qual_type);
   if (tag_type)
     return tag_type->isBeingDefined();
   return false;
 }
 
 bool ClangASTContext::IsObjCObjectPointerType(const CompilerType &type,
                                               CompilerType *class_type_ptr) {
-  if (!type)
+  if (!ClangUtil::IsClangType(type))
     return false;
 
   clang::QualType qual_type(ClangUtil::GetCanonicalQualType(type));
 
   if (!qual_type.isNull() && qual_type->isObjCObjectPointerType()) {
     if (class_type_ptr) {
       if (!qual_type->isObjCClassType() && !qual_type->isObjCIdType()) {
         const clang::ObjCObjectPointerType *obj_pointer_type =

lldb/source/Symbol/ClangUtil.cpp

 
 #include "lldb/Symbol/ClangUtil.h"
 #include "lldb/Symbol/ClangASTContext.h"
 
 using namespace clang;
 using namespace lldb_private;
 
 bool ClangUtil::IsClangType(const CompilerType &ct) {
+  // Invalid types are never Clang types.
+  if (!ct)
+    return false;
+
   if (llvm::dyn_cast_or_null<ClangASTContext>(ct.GetTypeSystem()) == nullptr)
     return false;
 
   if (!ct.GetOpaqueQualType())
     return false;
 
   return true;
 }