This commit adds supports for clang to remap macOS availability attributes that have introduced,
deprecated or obsoleted versions to appropriate Mac Catalyst availability attributes. This
mapping is done using the version mapping provided in the macOS SDK, in the SDKSettings.json file.
The mappings in the SDKSettings json file will also be used in the clang driver for the driver
Mac Catalyst patch, and they could also be used in the future for other platforms as well.
Differential Revision: https://reviews.llvm.org/D105257
In Xcode 11, ld added a new flag called -platform_version that can be used instead of the old -<platform>_version_min flags.
The new flag allows Clang to pass the SDK version from the driver to the linker.
This patch adopts the new -platform_version flag in Clang, and starts using it by default,
unless a linker version < 520 is passed to the driver.
Differential Revision: https://reviews.llvm.org/D71579