Enabled 'unused ivars' check by default.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@54052 91177308-0d34-0410-b5e6-96231b3b80d8

utils/scan-build

@@ -100,7 +100,8 @@ my %AnalysesDefaultEnabled = (
   '-warn-dead-stores' => 1,
   '-checker-cfref' => 1,
   '-warn-objc-methodsigs' => 1,
-  '-warn-objc-missing-dealloc' => 1
+  '-warn-objc-missing-dealloc' => 1,
+  '-warn-objc-unused-ivars' => 1
 );
 
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