Check libpng directly into third_party/

third_party/libpng/scripts/intprefix.c

Index: third_party/libpng/scripts/intprefix.c
diff --git a/third_party/libpng/scripts/intprefix.c b/third_party/libpng/scripts/intprefix.c
new file mode 100644
index 0000000000000000000000000000000000000000..254f8e94b45e97d7c1e050d5406fbdcf0a9ccff4
--- /dev/null
+++ b/third_party/libpng/scripts/intprefix.c
@@ -0,0 +1,22 @@
+
+/* intprefix.c - generate an unprefixed internal symbol list
+ *
+ * Last changed in libpng version 1.6.16 [December 22, 2014]
+ * Copyright (c) 2013-2014 Glenn Randers-Pehrson
+ *
+ * This code is released under the libpng license.
+ * For conditions of distribution and use, see the disclaimer
+ * and license in png.h
+ */
+
+#define PNG_INTERNAL_DATA(type, name, array)\
+        PNG_DFN "@" name "@"
+
+#define PNG_INTERNAL_FUNCTION(type, name, args, attributes)\
+        PNG_DFN "@" name "@"
+
+#define PNG_INTERNAL_CALLBACK(type, name, args, attributes)\
+        PNG_DFN "@" name "@"
+
+#define PNGPREFIX_H /* self generation */
+#include "../pngpriv.h"