lib/rbtree: enable userland test suite for rbtree related data structure

Patch series "lib/interval_tree: add some test cases and cleanup", v2.

Since rbtree/augmented tree/interval tree share similar data structure,
besides new cases for interval tree, this patch set also does cleanup for
others.


This patch (of 7):

Currently we have some tests for rbtree related data structure, e.g. 
rbtree, augmented rbtree, interval tree, in lib/ as kernel module.

To facilitate the test and debug for those fundamental data structure,
this patch enable those tests in userland.

Link: https://lkml.kernel.org/r/20250310074938.26756-1-richard.weiyang@gmail.com
Link: https://lkml.kernel.org/r/20250310074938.26756-2-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michel Lespinasse <michel@lespinasse.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/include/linux/math64.h

@@ -72,4 +72,9 @@ static inline u64 mul_u64_u64_div64(u64 a, u64 b, u64 c)
 }
 #endif
 
+static inline u64 div_u64(u64 dividend, u32 divisor)
+{
+	return dividend / divisor;
+}
+
 #endif /* _LINUX_MATH64_H */