🚨 fix C4100 warnings

test/src/unit-allocator.cpp

@@ -100,9 +100,6 @@ struct my_allocator : std::allocator<T>
         std::allocator<T>::deallocate(p, n);
     }
 
-    // the code below warns about p in MSVC 2015 - this could be a bug
-    DOCTEST_MSVC_SUPPRESS_WARNING_PUSH
-    DOCTEST_MSVC_SUPPRESS_WARNING(4100)
     void destroy(T* p)
     {
         if (next_destroy_fails)
@@ -111,9 +108,9 @@ struct my_allocator : std::allocator<T>
             throw std::bad_alloc();
         }
 
+        static_cast<void>(p); // fix MSVC's C4100 warning
         p->~T();
     }
-    DOCTEST_MSVC_SUPPRESS_WARNING_POP
 
     template <class U>
     struct rebind