[libcxx] [test] Silence MSVC's spurious "warning C4100: 'p': unreferenced formal parameter".

[STL_MSFT]

Summary

Silence MSVC's spurious "warning C4100: 'p': unreferenced formal parameter".

This is a C1XX bug, tracked by VSO#188582. C1XX has found some good issues, so I would like to ask for this one-line warning suppression to make my life easier.

[EricWF]

Fix your compiler though!

[EricWF]

r273350.

test/support/test_allocator.h

size_type max_size() const throw()
         {return UINT_MAX / sizeof(T);}
 #if TEST_STD_VER < 11
     void construct(pointer p, const T& val)
         {::new(static_cast<void*>(p)) T(val);}
 #else
     template <class U> void construct(pointer p, U&& val)
         {::new(static_cast<void*>(p)) T(std::forward<U>(val));}
 #endif
-    void destroy(pointer p) {p->~T();}
+    void destroy(pointer p)
+        {
+            p->~T();
+            ((void)p); // Prevent MSVC's spurious unused warning
+        }
     friend bool operator==(const test_allocator& x, const test_allocator& y)
         {return x.data_ == y.data_;}
     friend bool operator!=(const test_allocator& x, const test_allocator& y)
         {return !(x == y);}
 };
 
 template <class T>
 class non_default_test_allocator