[jdk17u] RFR: 8372534: Update Libpng to 1.6.51

[Andrew John Hughes]

On Mon, 22 Dec 2025 08:20:20 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> > Update to the latest version of libpng. Changes from `Awt2dLibraries.gmk` were dropped as warnings are not split by file in 17u (missing [JDK-8294466](https://bugs.openjdk.org/browse/JDK-8294466)) and there are still unused warnings from `splashscreen_impl.c` in both 17u & 21u. The change built fine with GCC 8 on RHEL 8.
> 
> Okay I see, you cannot remove the warning disabling.

No, not as it stands (I did try). We could backport [JDK-8294466](https://bugs.openjdk.org/browse/JDK-8294466) - I was actually surprised to find that the underlying support for it is already there but only used by HotSpot - but that's something for 17u-dev after this.

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PR Comment: https://git.openjdk.org/jdk17u/pull/415#issuecomment-3682326403