Implement: <rdar://problem/6351970> rule request: warn if @synchronized mutex can be nil

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@113573 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Checker/GRExprEngine.cpp b/lib/Checker/GRExprEngine.cpp
index 851f34e..160ee46 100644
--- a/lib/Checker/GRExprEngine.cpp
+++ b/lib/Checker/GRExprEngine.cpp
@@ -373,6 +373,7 @@
   RegisterUndefCapturedBlockVarChecker(Eng);
   RegisterUndefResultChecker(Eng);
   RegisterStackAddrLeakChecker(Eng);
+  RegisterObjCAtSyncChecker(Eng);
 
   // This is not a checker yet.
   RegisterNoReturnFunctionChecker(Eng);