[libc++][test] Change IsSmallObject's calculation for std::any's small object buffer

[CaseyCarter]

Summary

sizeof(std::any) - sizeof(void*) is correct for both libc++ and the MSVC standard library.

[CaseyCarter]

libcxx/test/support/any_helpers.h

29

I have no idea why this line is highlighted: there are no changes on this line in the diff I submitted, the line endings are plain LF, ... :shrug:

[EricWF]

libcxx/test/support/any_helpers.h

36

LGTM.

libcxx/test/support/any_helpers.h

 #define RTTI_ASSERT(X) assert(X)
 #else
 #define RTTI_ASSERT(X)
 #endif
 
 template <class T>
   struct IsSmallObject
     : public std::integral_constant<bool
-        , sizeof(T) <= (sizeof(void*)*3)
+        , sizeof(T) <= sizeof(std::any) - sizeof(void*)
           && std::alignment_of<void*>::value
              % std::alignment_of<T>::value == 0
           && std::is_nothrow_move_constructible<T>::value
         >
   {};
 
 template <class T>
 bool containsType(std::any const& a) {
 #if !defined(TEST_HAS_NO_RTTI)
     return a.type() == typeid(T);
 #else
     return a.has_value() && std::any_cast<T>(&a) != nullptr;
 #endif
 }