This copies the [behavior of meson](https://github.com/microsoft/vcpkg/blob/f4b1530fea04e448e443c60d2ae385adcf616598/scripts/cmake/vcpkg_configure_meson.cmake#L140) which depends on `CMAKE_OSX_SYSROOT` and `VCPKG_OSX_ARCHITECTURES` which are only available on osx.  