Keep track of whether a class is abstract or not. This is currently only used for the __is_abstract type trait.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67461 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/DeclCXX.cpp b/lib/AST/DeclCXX.cpp
index 5e9b0cd..33e870b 100644
--- a/lib/AST/DeclCXX.cpp
+++ b/lib/AST/DeclCXX.cpp
@@ -27,8 +27,8 @@
   : RecordDecl(K, TK, DC, L, Id),
     UserDeclaredConstructor(false), UserDeclaredCopyConstructor(false),
     UserDeclaredCopyAssignment(false), UserDeclaredDestructor(false),
-    Aggregate(true), PlainOldData(true), Polymorphic(false), Bases(0),
-    NumBases(0), Conversions(DC, DeclarationName()) { }
+    Aggregate(true), PlainOldData(true), Polymorphic(false), Abstract(false),
+    Bases(0), NumBases(0), Conversions(DC, DeclarationName()) { }
 
 CXXRecordDecl *CXXRecordDecl::Create(ASTContext &C, TagKind TK, DeclContext *DC,
                                      SourceLocation L, IdentifierInfo *Id,