cl: link go name

cl/_testrt/linkname/in.go

@@ -0,0 +1,15 @@
+package main
+
+import (
+	_ "unsafe"
+
+	"github.com/goplus/llgo/internal/runtime/c"
+)
+
+//go:linkname print github.com/goplus/llgo/cl/internal/linktarget.F
+func print(a, b, c, d *c.Char)
+
+func main() {
+	print(c.Str("a"), c.Str("b"), c.Str("c"), c.Str("d"))
+	print(c.Str("1"), c.Str("2"), c.Str("3"), c.Str("4"))
+}