update png configuration.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1323 bbd45198-f89e-11dd-88c7-29a3b14d5316

components/external/libpng/pngconf.h

@@ -20,13 +20,17 @@
 #define __RT_THREAD__
 
 #ifdef __RT_THREAD__
+#include <rtthread.h>
+#define PNG_MAX_MALLOC_64K
+
+#ifndef RT_USING_NEWLIB
 #define PNG_NO_WRITE_SUPPORTED
 #define PNG_NO_STDIO
 #define PNG_NO_SETJMP_SUPPORTED
-#define PNG_MAX_MALLOC_64K
 #define malloc	rtgui_malloc
 #define free	rtgui_free
 #endif
+#endif
 
 #define PNG_1_2_X