[coroutines] Store an address of destroy OR cleanup part in the coroutine frame.

[coroutines] Store an address of destroy OR cleanup part in the coroutine frame.

Summary:
If heap allocation of a coroutine is elided, we need to make sure that we will update an address stored in the coroutine frame from f.destroy to f.cleanup.
Before this change, CoroSplit synthesized these stores after coro.begin:

```
    store void (%f.Frame*)* @f.resume, void (%f.Frame*)** %resume.addr
    store void (%f.Frame*)* @f.destroy, void (%f.Frame*)** %destroy.addr

```

In those cases where we did heap elision, but were not able to devirtualize all indirect calls, destroy call will attempt to "free" the coroutine frame stored on the stack. Oops.

Now we use select to put an appropriate coroutine subfunction in the destroy slot. As bellow:

```
    store void (%f.Frame*)* @f.resume, void (%f.Frame*)** %resume.addr
    %0 = select i1 %need.alloc, void (%f.Frame*)* @f.destroy, void (%f.Frame*)* @f.cleanup
    store void (%f.Frame*)* %0, void (%f.Frame*)** %destroy.addr
```

Reviewers: majnemer

Subscribers: mehdi_amini, llvm-commits

Differential Revision: https://reviews.llvm.org/D25377

llvm-svn: 283625