cl: funcOf; use gogen/packages.Importer

cl/_testdata/_importpkg/in.go

@@ -0,0 +1,9 @@
+package main
+
+import "github.com/goplus/llgo/cl/internal/stdio"
+
+var hello = [...]int8{'H', 'e', 'l', 'l', 'o', '\n', 0}
+
+func main() {
+	stdio.Printf(&hello[0])
+}