Define _DEBUG to 0 if not done yet

to avoid the preprocess warning

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: I4ae1eb8533563d377ec8614f0c9428c8734e1f2c

tlsf.c

@@ -7,6 +7,10 @@
 
 #include "tlsf.h"
 
+#if !defined(_DEBUG)
+#define _DEBUG 0
+#endif
+
 #if defined(__cplusplus)
 #define tlsf_decl inline
 #else
@@ -1046,7 +1050,7 @@ void tlsf_remove_pool(tlsf_t tlsf, pool_t pool)
 */
 
 #if _DEBUG
-int test_ffs_fls()
+static int test_ffs_fls()
 {
 	/* Verify ffs/fls work properly. */
 	int rv = 0;