Add EIGEN_UNUSED_VARIABLE to unused variable in Memory.h

Eigen/src/Core/util/Memory.h

diff --git a/Eigen/src/Core/util/Memory.h b/Eigen/src/Core/util/Memory.h
index 0b9589c..258c391 100644
--- a/Eigen/src/Core/util/Memory.h
+++ b/Eigen/src/Core/util/Memory.h
@@ -83,6 +83,7 @@
     new int[huge];
     #else
     void* unused = ::operator new(huge);
+    EIGEN_UNUSED_VARIABLE(unused);
     #endif
   #endif
 }