[BUILD] make ebtree headers multiple-include compatible
ebtree did not support being included multiple times.
diff --git a/doc/internals/ebtree b/doc/internals/ebtree
index dd1beda..3b624d4 100644
--- a/doc/internals/ebtree
+++ b/doc/internals/ebtree
@@ -12,3 +12,5 @@
and likely/unlikely which are used in ebtree are also used and defined
in haproxy. Thus, we just conditionally define them.
+Last, all eb*tree*.h have been adapted to support being included multiple
+times, using #ifndef/#define/#endif.