builtin identifiers cannot be shadowed

[thehowl]

package main

func main() {
	rune := rune('x')
	println(rune)
}

$ gno run x.gno
--- preprocess stack ---
stack 2: func main() { rune<VPBlock(1,0)> := rune<VPUverse(0)>('x'); println<VPUverse(0)>(rune<VPUverse(0)>) }
stack 1: file{ package main; func main() { rune<VPBlock(1,0)> := rune<VPUverse(0)>('x'); println<VPUverse(0)>(rune<VPUverse(0)>) } }
stack 0: package(main)
------------------------
panic: expected block value path type [recovered]
        panic: main/x.gno:4: expected block value path type

goroutine 1 [running]:
github.com/gnolang/gno/gnovm/pkg/gnolang.Preprocess.func2.1()
        /home/howl/oc/gno/gnovm/pkg/gnolang/preprocess.go:173 +0x46d
panic({0xbf0b00, 0xf4bfc0})
        /usr/lib/go/src/runtime/panic.go:890 +0x263
github.com/gnolang/gno/gnovm/pkg/gnolang.fillNameExprPath({0xf62ed8, 0xc000581800}, 0xc0001716d0, 0x4?)
        /home/howl/oc/gno/gnovm/pkg/gnolang/preprocess.go:3218 +0x2c7

(note: one can even technically "shadow" in a global package's scope, like in this example)