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.
The plugin layouts are different across platforms. Move this into a
virtual method and allow replacement. On Windows, the plugins are
placed into the `bin` directory as the DLLs should always be co-located
to ensure that the proper DLLs are found (there is no concept of RPATH).
'load-plugin-library', 'load-plugin-executable', '-plugin-path' and
'-external-plugin-path' should be searched in the order they are
specified in the arguments.
Previously, for example '-plugin-path' used to precede
'-external-plugin-path' regardless of the position in the arguments.
