[3nids]

Allows building x64-osx-dynamic packages on an arm64 macOS machine (--host-triplet=arm64-osx-dynamic --triplet=x64-osx-dynamic), running the x86_64 target tools under Rosetta. The motivation is building qtwebengine + py-pyqt6 + py-pyqt6-webengine without an Intel runner.

On macOS, vcpkg's toolchain sets CMAKE_CROSSCOMPILING=OFF for arm64 -> x64 (the target binaries can run), but VCPKG_CROSSCOMPILING is still on. That mismatch breaks several ports here:

• python3: CPython's configure refuses --host=x86_64-apple-darwin --build=aarch64-apple-darwin ("cross build not supported"). On a macOS host the port now configures as a native build.
• vcpkg-python-scripts: the py-* ports run the target python, but gpep517, installer, setuptools and wheel are host dependencies, so the build fails with No module named gpep517. In a cross build the host site-packages (pure Python only) is appended to PYTHONPATH. This only works because the target python can run on the build machine, so it is not a general answer to Crosscompiling python extensions using host python #39.
• python3 (pipe2): with a macOS 27 SDK on macOS 26, CPython 3.12 detects pipe2, links it weakly and calls it unguarded, so os.pipe() and subprocess segfault. ac_cv_func_pipe2=no on macOS avoids it. This is not cross-specific; it affects native builds with a newer SDK than the running OS.
• py-pyqt6, py-pyqt6-webengine, py-qscintilla: sipbuild needs a target qmake, which doesn't exist in a cross build (qtbase builds no host tools). New helper vcpkg_python_get_qmake returns the installed qmake if present, otherwise a wrapper that runs the host qmake with the target qt.conf, the same way vcpkg_qmake_configure does.

The last commit bumps port-version of the touched ports.

Tested on macOS 26.6 / Xcode 27.2 on an arm64 host, vcpkg master afa249f12, release-only triplets (x64-osx-dynamic-release target, arm64-osx-dynamic-release host). qtwebengine[webengine,webchannel,pdf] (3.7 h, no changes to its port), py-pyqt6 (qtdeclarative, qtwebengine) and py-pyqt6-webengine all built. All 346 Mach-O files in the target tree are x86_64-only with no build-directory paths in load commands, PyQt6.QtWebEngine{Core,Widgets,Quick} import under arch -x86_64, and a QWebEnginePage loads a page and evaluates JavaScript.

Not tested: this repository's CI (there is no cross job), debug builds, other ports with C extensions (numpy, scipy, ...), non-macOS cross builds. Native builds should be unaffected apart from the pipe2 change, but I have not re-run them with these changes. I can add a cross job to macos.yml if wanted.

[m-kuhn]

LGTM so far, before merging please add tests for (macos) cross builds, probably as replacement for the existing intel builds

[3nids]

Replaced by #299 with the same commits. The branch moved to this repository so that #300 can be stacked on it.