cl: go:linkname specifies call convention by C.xxx

cl/_testdata/method/in.go

@@ -8,7 +8,7 @@ func (a T) Add(b T) T {
 	return a + b
 }
 
-//go:linkname printf printf
+//go:linkname printf C.printf
 func printf(format *int8, __llgo_va_list ...any)
 
 var format = [...]int8{'H', 'e', 'l', 'l', 'o', ' ', '%', 'd', '\n', 0}