RFR: 8372534: Update Libpng to 1.6.51

[Jayathirth D V]

On Thu, 27 Nov 2025 01:12:48 GMT, Jayathirth D V <jdv at openjdk.org> wrote:

> Upgrade libpng used for Splashscreen from 1.6.47 to 1.6.51 version.

make/modules/java.desktop/lib/ClientLibraries.gmk line 240:

> 238:       DISABLED_WARNINGS_gcc_jcmaster.c := implicit-fallthrough, \
> 239:       DISABLED_WARNINGS_gcc_jdphuff.c := shift-negative-value, \
> 240:       DISABLED_WARNINGS_gcc_png.c := maybe-uninitialized, \

These warnings were disabled in previous libpng update because of https://github.com/openjdk/jdk/pull/24021/files#r1993813117

We have appropriate update in upstream and we are not facing the build issue, so the code change is reverted.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28518#discussion_r2566971834