fix cjson warning: "true" and "false redefined

the similar change also exist in the offical git:
https://github.com/DaveGamble/cJSON

Part of #935.

Change-Id: I3d98de3ec893ccf0b0cab37acc2dbfef00d9e2b6
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
(cherry picked from commit 98c868360c858f4c5fd466bd03fd157ac56b3f06)
Signed-off-by: Bruce A. Mah <bmah@es.net>

src/cjson.c

@@ -47,7 +47,14 @@
 #include "cjson.h"
 
 /* define our own boolean type */
+#ifdef true
+#undef true
+#endif
 #define true ((cJSON_bool)1)
+
+#ifdef false
+#undef false
+#endif
 #define false ((cJSON_bool)0)
 
 typedef struct {