QF1011 gets untyped constants wrong

[dominikh]

For

package main

const X = 1

func main() {
	var _ uint = X
}

we currently emit

sand.go:6:8: could omit type uint from declaration; it will be inferred from the right-hand side (QF1011)

which is clearly wrong. X is an untyped constant, and without the explicit uint, it will default to int.

The issue lies with how we check the type of the RHS. The type-checker "helpfully" types that use of X for us, based on its context.

(This bug feels very familiar, I think we've fixed pretty much the same issue in another check recently.)