Fixes T88419 Build opens on macOS 10.14. Can be downloaded from
https://builder.blender.org/download/experimental/ tmp-macminver
CMAKE_OSX_DEPLOYMENT_TARGET is now always the same as
OSX_MIN_DEPLOYMENT_TARGET. I don't know the historical reason of
why they were allowed to be different.
MACOSX_DEPLOYMENT_TARGET has been moved to platform_apple_xcode
because it's helpful to deduce CMAKE_OSX_DEPLOYMENT_TARGET [1] and
platform_apple is included after platform_apple_xcode. Although it seems
useless now that we're explicitly setting CMAKE_OSX_DEPLOYMENT_TARGET.
Remove it ? man clang says that MACOSX_DEPLOYMENT_TARGET is used
if mmacosx-version-min is not present.
Docs suggest that CMAKE_OSX_DEPLOYMENT_TARGET should be set before
project call. Should we do that, like in D10838, using
blender_project_hack_pre ?
[1]: https://cmake.org/cmake/help/latest/variable/CMAKE_OSX_DEPLOYMENT_TARGET.html]