* Allow normal function results of @yield_once coroutines
* Address review comments
* Workaround LLVM coroutine codegen problem: it assumes that unwind path never returns.
This is not true to Swift coroutines as unwind path should end with error result.
This adds SIL-level support and LLVM codegen for normal results of a coroutine.
The main user of this will be autodiff as VJP of a coroutine must be a coroutine itself (in order to produce the yielded result) and return a pullback closure as a normal result.
For now only direct results are supported, but this seems to be enough for autodiff purposes.
A lot of attributes are essentially default target configuration, and we should only differ when there's a good reason to.
For the attributes we were already setting:
- the ptrauth and target CPU/feature attributes are taken care of by Clang
- I've updated the optsize/minsize attributes to the apparent intent
- I've left the frame-pointer override in place for now
Fixes rdar://63289339, which was caused by Swift's ptrauth IR attributes getting out of sync with Clang's.
