radix tree test suite: add lockdep_is_held to header

maple tree uses lockdep_is_held, so define it as external in the header.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Liam R. Howlett <[e-mail]>
Tested-by: Yu Zhao <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: David Howells <[e-mail]>
Cc: Davidlohr Bueso <[e-mail]>
Cc: "Matthew Wilcox (Oracle)" <[e-mail]>
Cc: SeongJae Park <[e-mail]>
Cc: Sven Schnelle <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Will Deacon <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/radix-tree/linux/lockdep.h

···
 					struct lock_class_key *key)
 {
 }
+
+extern int lockdep_is_held(const void *);
 #endif /* _LINUX_LOCKDEP_H */