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

cl/_testdata/printf/in.go

@@ -2,7 +2,7 @@ package main
 
 import _ "unsafe"
 
-//go:linkname printf printf
+//go:linkname printf C.printf
 func printf(format *int8, __llgo_va_list ...any)
 
 var hello = [...]int8{'H', 'e', 'l', 'l', 'o', '\n', 0}