BUILD: ebtree: don't redefine types u32/s32 in scope-aware trees

Clang emits a warning about these types being redefined in eb32sctree
while they are already defined in eb32tree. Let's simply not redefine
them if eb32tree was already included.

ebtree/eb32sctree.h

@@ -28,8 +28,10 @@
 #define eb32sc_entry(ptr, type, member) container_of(ptr, type, member)
 
 /* These types may sometimes already be defined */
+#ifndef _EB32TREE_H
 typedef unsigned int u32;
 typedef   signed int s32;
+#endif
 
 /* This structure carries a node, a leaf, a scope, and a key. It must start
  * with the eb_node so that it can be cast into an eb_node. We could also