[jdk8u-dev] RFR: 8328999: Update GIFlib to 5.2.2

[Andrew John Hughes]

This updates the in-tree giflib to 5.2.2. The actual code changes are a clean backport, but the license file changes needed adapting from the `giflib.md` file in 11u and later to the `THIRD_PARTY_README` file in 8u (now only one copy following [JDK-8338144](https://bugs.openjdk.org/browse/JDK-8338144))

8u is also missing [JDK-8225487](https://bugs.openjdk.org/browse/JDK-8225487) which I've included as part of this patch. This updates the license to credit `openbsd-reallocarray.c` and is updated further by 8238999. I also included changes made by the 5.2.1 update which were missed because 8225487 was missing.

The `giflib.md` changes include some odd changes, replacing the giflib VCS URL with just `tree/README`. I've raised [8339271](https://bugs.openjdk.org/browse/JDK-8339271) to correct this.

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Commit messages:
 - Backport bc8aeb6496b7e86d1f616d4c1b7c26f172c1dd8a

Changes: https://git.openjdk.org/jdk8u-dev/pull/571/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=571&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328999
  Stats: 847 lines in 8 files changed: 182 ins; 105 del; 560 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/571.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/571/head:pull/571

PR: https://git.openjdk.org/jdk8u-dev/pull/571