With `ARCMigrate` and `arcmt-test` removed from clang in
https://github.com/llvm/llvm-project/pull/119269 and the new code
migration experience under way (see
https://github.com/swiftlang/swift-evolution/pull/2673), these options
are no longer relevant nor known to be in use. They were introduced
long ago to support fix-it application in Xcode.
For now, turn them into a no-op and emit a obsoletion warning.
(cherry picked from commit 46c394788a84d5932289c71274dd32ea2d61d9dc)
Find all the usages of `--enable-experimental-feature` or
`--enable-upcoming-feature` in the tests and replace some of the
`REQUIRES: asserts` to use `REQUIRES: swift-feature-Foo` instead, which
should correctly apply to depending on the asserts/noasserts mode of the
toolchain for each feature.
Remove some comments that talked about enabling asserts since they don't
apply anymore (but I might had miss some).
All this was done with an automated script, so some formatting weirdness
might happen, but I hope I fixed most of those.
There might be some tests that were `REQUIRES: asserts` that might run
in `noasserts` toolchains now. This will normally be because their
feature went from experimental to upcoming/base and the tests were not
updated.
