cl: fake libc

cl/_testcgo/hello/in.go

@@ -0,0 +1,10 @@
+package main
+
+import "github.com/goplus/llgo/cl/internal/libc"
+
+var format = [...]int8{'H', 'e', 'l', 'l', 'o', ' ', '%', 'd', '\n', 0}
+
+func main() {
+	sfmt := &format[0]
+	libc.Printf(sfmt, libc.Strlen(sfmt))
+}