8372534: Update Libpng to 1.6.51

[gnu-andrew]

Update to the latest version of libpng. Clean backport which built fine with GCC 11 on RHEL 8.

---

Progress

• Change must not contain extraneous whitespace
• JDK-8372534 needs maintainer approval
• Commit message must refer to an issue

Issue

• JDK-8372534: Update Libpng to 1.6.51 (Bug - P3 - Requested)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk25u-dev.git pull/56/head:pull/56
$ git checkout pull/56

Update a local copy of the PR:
$ git checkout pull/56
$ git pull https://git.openjdk.org/jdk25u-dev.git pull/56/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 56

View PR using the GUI difftool:
$ git pr show -t 56

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk25u-dev/pull/56.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back andrew! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[openjdk]

⚠️ @gnu-andrew This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[mlbridge]

Webrevs

• 00: Full (c6281ddd)

[gnu-andrew]

/approval request Regular update for the in-tree copy of libpng. The backport from 26 is clean and GHA builds & testing have passed.

[openjdk]

@gnu-andrew
8372534: The approval request has been created successfully.