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

[zgu at redhat.com]

Changeset: 75fe7bdb490f
Author:    zgu
Date:      2019-09-12 15:20 -0400
URL:       https://hg.openjdk.java.net/jdk8u/jdk8u-dev/corba/rev/75fe7bdb490f

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

! THIRD_PARTY_README