Apparently `-fvisibility=hidden` is not sufficient to hide some of the
symbols in this library. I've explicitly marked the symbols that were
flagged as being incorrectly exported as "hidden" so hopefully no one
drags them out again.
This is a statically linked library, so the symbols shouldn't need to be
exported for this work work. To ensure that this is the case and that
we're still hitting the overridden API with all of the hidden symbols, I
added a debug log line to the fixed `AsyncTask::waitFuture`
implementation and have verified that we see the compat56 log message
emitted from executables that need the compat56 library.
Symbols from the backdeploy libraries shouldn't be exported by dylibs.
Also found an undefined declaration (asyncMainDrainQueue) and a
duplicate declaration for `swift_task_getCurrent`, so those were cleaned
up.
This patch gets everything to the point of building the library, but it
doesn't run yet since I have missing symbols.
Unlike previous compatibility libraries and the concurrency
compatibility library, I'm organizing the headers a bit more. This is
because we're merging the two libraries into one. They share some common
header names, and while I could rename them for namespacing purposes,
it's easier to just use a directory structure for this.
The `include/Runtime` and corresponding `Runtime/` directories are for
backdeployed changes to the stdlib itself.
The `include/Concurrency` and corresponding `Concurrency/` directories
are for backdeployed changes to the concurrency runtimes.
