compiler: Add FIELD_SIZEOF helper

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

include/common/compiler.h

@@ -57,6 +57,10 @@
 	const typeof( ((type *)0)->member ) *__mptr = (ptr);	\
 	(type *)( (char *)__mptr - offsetof(type,member) );})
 
+#ifndef FIELD_SIZEOF
+# define FIELD_SIZEOF(t, f)	(sizeof(((t*)0)->f))
+#endif
+
 #define __round_mask(x, y)	((__typeof__(x))((y) - 1))
 #define round_up(x, y)		((((x) - 1) | __round_mask(x, y)) + 1)
 #define round_down(x, y)	((x) & ~__round_mask(x, y))