As a fly-by, also remove a superfluous <cstddef> include in promote.h.
Differential Revision: https://reviews.llvm.org/D142657
#include <__type_traits/integral_constant.h>
#include <__type_traits/is_same.h>
#include <__utility/declval.h>
-#include <cstddef>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#include <__type_traits/is_constant_evaluated.h>
#include <__type_traits/is_floating_point.h>
#include <__type_traits/is_same.h>
+#include <__type_traits/promote.h>
#include <__type_traits/remove_cv.h>
#include <version>