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

cl/_testcgo/strlen/in.go

@@ -3,10 +3,10 @@ package main
 import "C"
 import _ "unsafe"
 
-//go:linkname printf printf
+//go:linkname printf C.printf
 func printf(format *int8, __llgo_va_list ...any)
 
-//go:linkname strlen strlen
+//go:linkname strlen C.strlen
 func strlen(str *int8) C.int
 
 var format = [...]int8{'H', 'e', 'l', 'l', 'o', ' ', '%', 'd', '\n', 0}