Add maybe-unused attribute to a variable.

Summary:
Mark a variable as maybe-unused to prevent a -Wunused-but-set-variable
warning in optimized builds where asserts are removed.Test/first commit
to check setup and understand patch submission process.

Reviewers: srhines, pirama, dblaikie

Reviewed By: dblaikie

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D49756

llvm-svn: 338654

lib/IR/SafepointIRVerifier.cpp

@@ -92,6 +92,7 @@ public:
         Listed = true;
       }
     }
+    (void)Listed;
     assert(Listed && "basic block is not found among incoming blocks");
     return false;
   }