[jdk11u-dev] RFR: 8209115: adjust libsplashscreen linux ppc64le builds for easier libpng update

[Goetz Lindenmaier]

When trying to backport 8295685: Update Libpng to 1.6.38 " I found this is needed to make 
it apply clean. All regular updates of png will profit from this.

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Commit messages:
 - Backport 8044814e305c53ff22ec1831411481c4f4dc1f62

Changes: https://git.openjdk.org/jdk11u-dev/pull/1682/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1682&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8209115
  Stats: 9 lines in 2 files changed: 6 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1682.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1682/head:pull/1682

PR: https://git.openjdk.org/jdk11u-dev/pull/1682