[Coro][Debuginfo] Add debug info to `__NoopCoro_ResumeDestroy` function

With this commit, we now attach an `DISubprogram` to the LLVM-generated
`_NoopCoro_ResumeDestroy` function. Thereby, lldb can show a
`std::coroutine_handle` to a `std::noop_coroutine` as

```
continuation = coro frame = 0x555555560d98 {
  resume = 0x0000555555555c50 (a.out`__NoopCoro_ResumeDestroy)
  destroy = 0x0000555555555c50 (a.out`__NoopCoro_ResumeDestroy)
}
```

instead of

```
continuation = coro frame = 0x555555560d98 {
  resume = 0x0000555555555c50 (a.out`___lldb_unnamed_symbol211)
  destroy = 0x0000555555555c50 (a.out`___lldb_unnamed_symbol211)
}
```

I renamed the function from `NoopCoro.ResumeDestroy` to
`_NoopCoro_ResumeDestroy` because:
* the leading `_` makes sure this is a reserved name and should not
  clash with any user-provided names
* the `.` was replaced by a `_`, so the name is now a valid identifier
  in C, making it allows me to type its name in the debugger

Differential Revision: https://reviews.llvm.org/D132580