Force macos cibuildwheel to use Xcode clang (#2315)

On GitHub’s macOS runners, clang on PATH often points to Homebrew’s
LLVM (e.g. /usr/local/opt/llvm@18/bin/clang) instead of Xcode’s clang.

That LLVM build pulls in Homebrew’s libunwind, which is built with
minimum macOS 14.0. When the OpenEXR extension is built with that
toolchain, it ends up depending on that libunwind.

During wheel repair, delocate copies all non-system dependencies into
the wheel. It then checks that each bundled library’s minimum macOS
version matches the wheel’s target. Homebrew’s libunwind requires
14.0, so if the wheel claims 11.0 (or 10.15), delocate fails.

Xcode’s clang lives at /usr/bin/clang and uses the system C++ runtime
and unwinder. Those are part of macOS and don’t bring in a separate
libunwind dylib with a higher minimum version.

Assisted-with: Cursor / Claude Opus 4.5

Signed-off-by: Cary Phillips <cary@ilm.com>

Author: cary-ilm

pyproject.toml

@@ -89,3 +89,6 @@ manylinux-aarch64-image = "manylinux2014"
 # Needed for full C++17 support
 [tool.cibuildwheel.macos.environment]
 MACOSX_DEPLOYMENT_TARGET = "10.15"
+# pass compilers directly to avoid Homebrew LLVM libunwind
+CMAKE_ARGS = "-DCMAKE_C_COMPILER=/usr/bin/clang -DCMAKE_CXX_COMPILER=/usr/bin/clang++"
+