Fixes 3572: macOS 13 runner is closing down

[pljones]

Short description of changes

Claude Haiku 4.5 suggested fixes for continued support of macOS 10.13+ with Qt5.

• move to macos-15 builder for macOS on Apple Silicon and iOS and macos-15-intel for main and legacy macOS on Intel
• move to Xcode 16.3.0
• use QMAKE_MACOSX_DEPLOYMENT_TARGET to target 11.0 for "modern" and 10.13 for "legacy" macOS builds (rather than 10.12 previously)
• retain existing Qt versions

CHANGELOG: Provide continued legacy macOS support (but moving Sierra to High Sierra as minimum target)

Context: Fixes an issue?

Fixes 3572

Does this change need documentation? What needs to be documented and how?

No - change log should be enough.

Note: You can find old (legacy) versions supporting outdated operating systems on the GitHub release page.

The website doesn't document what "old (legacy) versions" means.

Status of this Pull Request

Needs reviewing by humans who know macOS (and potentially iOS).

What is missing until this pull request can be merged?

No testing has been done. So someone with a legacy mac needs to try it. Hopefully it'll actually build...

Checklist

• I've verified that this Pull Request follows the general code principles
• I tested my code and it does what I want
• My code follows the style guide
• I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
• I've filled all the content above

AUTOBUILD: Please build all targets

[pljones]

OK, Claude Haiku 4.5 has failed to find a solution (using up 92% of my CoPilot chat allowance for a month that resets in 29 days).

[ann0see]

Legacy runs on the latest version of macOS (26.2) (apple silicon Mac)

[ann0see]

Qt 5 even works fine with macOS 26 and Xcode 26 (latest version as of December 2025). So I believe it's ok to push the legacy build even further.

[ann0see]

ld: framework 'AGL' not found

on macOS?
That's weird. A local build seemed to work on 26.2 (Apple Silicon real machine).

Hmm maybe I tested with Qt5 only. But now I get another error on macOS (local build):

clang: error: unsupported option '-msse' for target 'arm64-apple-darwin25.2.0'

Let's not move the non legacy build then.

[pljones]

Don't say our Linux build's gone stale, too...

(I'm running Qt 6.10.1 on Ubuntu 24.4 LTS and I don't know what we target for RPi users.)

[pljones]

@ann0see I'll leave the Xcode/AGL problem to you -- the iOS and macOS Legacy now work, thanks.

I've cleaned things up and squashed what was left to a single commit against main.

[pljones]

OK, well, it builds now.

Anyone for testing it?