Restore macOS 10.13 (High Sierra) support

[justin-espedal]

This restores macOS 10.13 support by ensuring that the pcre code that's linked into Haxe is built from source with the 10.13 deployment target.

This fixes https://github.com/HaxeFoundation/haxe/issues/10723

[justin-espedal]

Since this was only a theoretical fix to the issue, I felt a little iffy about sending a PR and stating that this "restores macOS 10.13 support" as a fact, so I marked it as a draft at first.

I've had the chance to confirm for myself that the binaries this PR produces do run on macOS 10.13, so this is ready to merge.

[Simn]

Could you update this PR so that we can check the CI again?

[justin-espedal]

I've updated it. 🫡

[Simn]

Thank you!