[PATCH] include: Use __builtin_offsetof on Clang.

[Jacek Caban]

Fixes a number of warning on MSVC target.

Signed-off-by: Jacek Caban <jacek(a)codeweavers.com>
---
  include/msvcrt/stddef.h | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)