rbtree: avoid redefining offsetof

Newer versions of gcc will define & export offsetof, so we don't
want to unconditionally define it.  Otherwise we hit:
	In file included from mkfs.jffs2.c:76:0:
	rbtree.h:134:0: warning: "offsetof" redefined
	/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.1/include/stddef.h:411:0: note:
		this is the location of the previous definition

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/rbtree.h b/rbtree.h
index 9597b10..e64dc9a 100644
--- a/rbtree.h
+++ b/rbtree.h
@@ -131,7 +131,10 @@ static inline void rb_set_color(struct rb_node *rb, int color)
 
 #define RB_ROOT	(struct rb_root) { NULL, }
 
+/* Newer gcc versions take care of exporting this */
+#ifndef offsetof
 #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
+#endif
 
 #define container_of(ptr, type, member) ({                      \
         const typeof( ((type *)0)->member ) *__mptr = (ptr);    \