Enable default @synthesize by default.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@152140 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Driver/ToolChains.h

@@ -349,7 +349,7 @@ public:
   }
   
   virtual bool IsObjCDefaultSynthPropertiesDefault() const {
-    return false;
+    return true;
   }
 
   virtual bool IsObjCNonFragileABIDefault() const {