We are now using a properly-substituted minimal deployment target
compiler flag (`%min_macos_deployment_target=10.11`). Enable test on
iOS and watchOS plus simulators. We are also not testing on very old
platforms anymore, so we can remove some obsolete lit infrastructure.
* Support macOS 11+ version scheme
* Standardize substitution name `%min_deployment_target=x.y`
* Remove unneeded error cases (the input version is hard-coded)
* Specify version as tuple instead of string; no need to parse it
These changes should also facilitate a future addition of a substitution
that expands to "set deployment target to current target version"
(https://reviews.llvm.org/D70151).
Reviewed By: delcypher
Differential Revision: https://reviews.llvm.org/D85925
Kazuaki Ishizaki