tools: add sizeof_field and endof_field macros

* `sizeof_field` returns the size of a specific struct member
* `endof_field` returns the offset to the end of the member within the struct

It will be useful in upcoming layout checks of SMBIOS structs.

Signed-off-by: Petr Beneš <w1benny@gmail.com>
Acked-by: Anthony PERARD <anthony.perard@vates.tech>

tools/include/xen-tools/common-macros.h

@@ -83,6 +83,11 @@
 #define __packed __attribute__((__packed__))
 #endif
 
+#define sizeof_field(type, member) sizeof(((type *)NULL)->member)
+
+#define endof_field(type, member) \
+    (offsetof(type, member) + sizeof_field(type, member))
+
 #define container_of(ptr, type, member) ({              \
     typeof(((type *)0)->member) *mptr__ = (ptr);        \
     (type *)((char *)mptr__ - offsetof(type, member));  \