Add bodge to get macOS build past CMake v4.1.1.

See #527.

Author: Tom Seddon

Makefile

@@ -45,6 +45,11 @@ INSTALLER:=
 ifdef OSX_DEPLOYMENT_TARGET
 CMAKE_DEFINES:=$(CMAKE_DEFINES) -DCMAKE_OSX_DEPLOYMENT_TARGET=$(OSX_DEPLOYMENT_TARGET)
 endif
+
+# Temporary bodge. Homebrew supplies CMake 4.1.1., and therefore the
+# GitHub CI runners use that.
+CMAKE_DEFINES:=$(CMAKE_DEFINES) -DCMAKE_POLICY_VERSION_MINIMUM=3.5
+
 # version number roulette.
 CLANG_FORMAT:=clang-format-mp-19