btreeTest: Fix build with gcc2.

src/tests/add-ons/kernel/file_systems/bfs/btree/cache.cpp

@@ -7,6 +7,7 @@
 
 #include "cache.h"
 
+#include <Debug.h>
 #include <File.h>
 #include <List.h>
 

src/tests/add-ons/kernel/file_systems/bfs/btree/cache.h

@@ -21,6 +21,8 @@ extern status_t cached_write(void* cache, off_t num, const void* _data,
 
 // Block Cache API
 
+extern "C" {
+
 extern const void* block_cache_get(void* _cache, off_t blockNumber);
 
 extern status_t block_cache_make_writable(void* _cache, off_t blockNumber,
@@ -32,4 +34,6 @@ extern status_t block_cache_set_dirty(void* _cache, off_t blockNumber,
 	bool dirty, int32 transaction);
 extern void block_cache_put(void* _cache, off_t blockNumber);
 
+} // extern "C"
+
 #endif	/* CACHE_H */