REPL 3.16.0 await block doesn't work

[vipero07]

Describe the bug
The REPL version 3.16.0 never resolves a promise.
https://svelte.dev/repl/dfacb2fa6dcc4c0aab18512e7fd189f3?version=3.16.0
vs
https://svelte.dev/repl/dfacb2fa6dcc4c0aab18512e7fd189f3?version=3.15.0

Information about your Svelte project:

• Your browser and the version: (e.x. Chrome 52.1, Firefox 48.0, IE 10)
  Chrome Version 74.0.3729.169 (Official Build) (64-bit)

• Your operating system: (e.x. OS X 10, Ubuntu Linux 19.10, Windows XP, etc)
  Windows 10

• Svelte version (Please check you can reproduce the issue with the latest release!)
  3.16.0

• Whether your project uses Webpack or Rollup
  REPL

Severity
It makes svelte look bad to people playing with the REPL, I'm not sure if this issue exists outside of the REPL in 3.16.0 itself, but its possible.

[ghost]

@Conduitry, this is a duplicate of #4044.
@vipero07, mind closing this in favor of the other one since work was already started?

[vipero07]

Seems to be related to using if blocks inside the await per @dkondrad and #4044