cl: _testdata/printf: almost done

cl/_testdata/printf/in.go

@@ -0,0 +1,12 @@
+package main
+
+import _ "unsafe"
+
+//go:linkname printf _printf
+func printf(format *int8, __llgo_va_list ...any)
+
+var hello = [...]int8{'H', 'e', 'l', 'l', 'o', '\n', 0}
+
+func main() {
+	printf(&hello[0])
+}