[CoroutineAccessors] Use retcon.once variant.

Allocate a coroutine frame in the caller based on the size in the
corresponding "function pointer" and pass it along with an allocator to
the callee.

include/swift/Runtime/RuntimeFunctions.def

@@ -2325,6 +2325,16 @@ FUNCTION(TaskDealloc,
          EFFECT(Concurrency),
          MEMEFFECTS(ArgMemOnly))
 
+// void swift_task_dealloc_through(void *ptr);
+FUNCTION(TaskDeallocThrough,
+         _Concurrency, swift_task_dealloc_through, SwiftCC,
+         CoroutineAccessorsAvailability,
+         RETURNS(VoidTy),
+         ARGS(Int8PtrTy),
+         ATTRS(NoUnwind),
+         EFFECT(Concurrency),
+         MEMEFFECTS(ArgMemOnly))
+
 // void swift_task_cancel(AsyncTask *task);
 FUNCTION(TaskCancel,
          _Concurrency, swift_task_cancel, SwiftCC,
@@ -2989,6 +2999,36 @@ FUNCTION(MemsetS, c, memset_s, C_CC, AlwaysAvailable,
          EFFECT(NoEffect),
          UNKNOWN_MEMEFFECTS)
 
+// void *swift_coro_alloc(CoroAllocator *, size_t size);
+FUNCTION(CoroAlloc,
+         _Concurrency, swift_coro_alloc, SwiftCC,
+         CoroutineAccessorsAvailability,
+         RETURNS(Int8PtrTy),
+         ARGS(CoroAllocatorPtrTy, SizeTy),
+         NO_ATTRS,
+         EFFECT(Allocating, Concurrency),
+         UNKNOWN_MEMEFFECTS)
+
+// void swift_coro_dealloc(CoroAllocator *, void *ptr);
+FUNCTION(CoroDealloc,
+         _Concurrency, swift_coro_dealloc, SwiftCC,
+         CoroutineAccessorsAvailability,
+         RETURNS(VoidTy),
+         ARGS(CoroAllocatorPtrTy, Int8PtrTy),
+         NO_ATTRS,
+         EFFECT(Deallocating, Concurrency),
+         UNKNOWN_MEMEFFECTS)
+
+// const CoroAllocator *swift_coro_getGlobalAllocator(CoroAllocatorFlags flags);
+FUNCTION(CoroGetGlobalAllocator, 
+         _Concurrency, swift_coro_getGlobalAllocator, SwiftCC, 
+         CoroutineAccessorsAvailability, 
+         RETURNS(CoroAllocatorPtrTy), 
+         ARGS(CoroAllocatorFlagsTy), 
+         ATTRS(NoUnwind, WillReturn), 
+         EFFECT(Allocating),
+         UNKNOWN_MEMEFFECTS)
+
 #undef RETURNS
 #undef ARGS
 #undef ATTRS