bcache-tools: list.h: only define offsetof() when it is undefined

For new gcc headers, offsetof() is defined, the definition in list.h
will be warned as redefined.

This patch checks whether offsetof() is defined, and only defines local
version of offsetof() when it is not defined by gcc headers.

Signed-off-by: Coly Li <colyli@suse.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/list.h b/list.h
index 55d2bb4d..458281d3 100644
--- a/list.h
+++ b/list.h
@@ -25,10 +25,12 @@
  */
 /*@{*/
 
+#ifndef offsetof
 /**
  * Get offset of a member
  */
 #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
+#endif /* offsetof*/
 
 /**
  * Casts a member of a structure out to the containing structure