std packages are a special case of the internal package check.
This test assumes that syscall.ByteSliceFromString refers to internal/bytealg.
-- go.mod --
module testdata
go 1.12
-- a/a.go --
package a
import "syscall"
var _, _ = syscall.ByteSliceFromString("") //@ inline(re"ByteSliceFromString", re`inaccessible package "internal/bytealg"`)