Not sure why you would ever do this, but it appears to be allowed by the
Go specification and previously TinyGo would crash with an unhelpful
error message when you would do this. I don't see any practical use of
it.
The implementation simply runs the builtin directly.
While LLVM coroutines are one implementation of goroutines, it is not
the only one. Therefore, rename the tests to 'goroutines' to better
describe what they're for.