Make the CXXDefaultArgExpr constructor protected and add a static Create function.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@79013 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index e9b1dd4..ced300b 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -2657,7 +2657,7 @@
       }
   
       // We already type-checked the argument, so we know it works.
-      Arg = new (Context) CXXDefaultArgExpr(FDecl->getParamDecl(i));
+      Arg = CXXDefaultArgExpr::Create(Context, FDecl->getParamDecl(i));
     }
     
     QualType ArgType = Arg->getType();