Merge topic 'apple-arch-sysroots' into release-3.17

84a1e67380 Apple: Fix mapping CMAKE_APPLE_ARCH_SYSROOTS to custom OSX_ARCHITECTURES
45fa9b32ca Apple: Improve handling of missing SDKs in CMAKE_APPLE_ARCH_SYSROOTS

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !4583