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.
When testing different linkers, it's sometimes useful to run the tests
with `SWIFT_DRIVER_TEST_OPTIONS=" -use-ld=<linker>"`. If we do this,
it will break a handful of tests because they expect the compiler driver
to choose an appropriate linker automatically.
To avoid having these fail, detect when someone has done this, and
set a new feature, `linker_overridden`, then mark the tests in question
with `UNSUPPORTED: linker_overridden`.
rdar://123504095
