FPII-2034: DO NOT MERGE Update libpng to 1.6.20

DO NOT MERGE Update libpng to 1.6.20

BUG:23265085
Change-Id: I2fc2106965c789a54f04412e9c63a0901b0c1e71
(cherry picked from commit 0b39f202aaedd3029e4270d2af7d58ba6634f9cd)
diff --git a/contrib/arm-neon/linux-auxv.c b/contrib/arm-neon/linux-auxv.c
index 696e297..4d26bd3 100644
--- a/contrib/arm-neon/linux-auxv.c
+++ b/contrib/arm-neon/linux-auxv.c
@@ -7,7 +7,7 @@
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
  * and license in png.h
- * 
+ *
  * SEE contrib/arm-neon/README before reporting bugs
  *
  * STATUS: COMPILED, TESTED