hg: jdk8u/jdk8u-dev: 8217676: Upgrade libpng to 1.6.37

[zgu at redhat.com]

Changeset: 4ca097c49b1b
Author:    zgu
Date:      2019-09-12 15:20 -0400
URL:       https://hg.openjdk.java.net/jdk8u/jdk8u-dev/rev/4ca097c49b1b

8217676: Upgrade libpng to 1.6.37
Reviewed-by: prr, jdv, kcr

! THIRD_PARTY_README