String.count -> UInt8 link fail

So far, the following sample code has failed in two separate projects for me:

```swift
let a = "asdf".count
let b = UInt8(a)
```

Compilation appears to succeed, but fail on the linking step. Let me know if you need more to go on.

Oh - working with espidf and compiling to an esp32c3, if any of that matters.