x/sys/windows: use SyscallN in mkwinsyscall

The mkwinsyscall command has a hard limit of 15 on the
number of syscall arguments. Windows has several system
calls with more than 15 arguments, for example CreateFontPackage
has 18 arguments.

If the number of arguments is higher than 15 we use SyscallN.

Updates golang/go#57914

windows/mkwinsyscall/mkwinsyscall.go

@@ -57,7 +57,6 @@ import (
 	"go/parser"
 	"go/token"
 	"io"
-	"io/ioutil"
 	"log"
 	"os"
 	"path/filepath"
@@ -568,6 +567,8 @@ func (f *Fn) SyscallParamCount() int {
 		return 12
 	case n <= 15:
 		return 15
+	case n <= 42: // current SyscallN limit
+		return n
 	default:
 		panic("too many arguments to system call")
 	}
@@ -578,11 +579,13 @@ func (f *Fn) Syscall() string {
 	c := f.SyscallParamCount()
 	if c == 3 {
 		return syscalldot() + "Syscall"
+	} else if c > 15 {
+		return syscalldot() + "SyscallN"
 	}
 	return syscalldot() + "Syscall" + strconv.Itoa(c)
 }
 
-// SyscallParamList returns source code for SyscallX parameters for function f.
+// SyscallParamList returns source code for SyscallN parameters for function f.
 func (f *Fn) SyscallParamList() string {
 	a := make([]string, 0)
 	for _, p := range f.Params {
@@ -923,7 +926,7 @@ func main() {
 	if *filename == "" {
 		_, err = os.Stdout.Write(data)
 	} else {
-		err = ioutil.WriteFile(*filename, data, 0644)
+		err = os.WriteFile(*filename, data, 0644)
 	}
 	if err != nil {
 		log.Fatal(err)
@@ -1011,7 +1014,7 @@ func {{.HelperName}}({{.HelperParamList}}) {{template "results" .}}{
 
 {{define "results"}}{{if .Rets.List}}{{.Rets.List}} {{end}}{{end}}
 
-{{define "syscall"}}{{.Rets.SetReturnValuesCode}}{{.Syscall}}(proc{{.DLLFuncName}}.Addr(), {{.ParamCount}}, {{.SyscallParamList}}){{end}}
+{{define "syscall"}}{{.Rets.SetReturnValuesCode}}{{.Syscall}}(proc{{.DLLFuncName}}.Addr(), {{if le .ParamCount 15}}{{.ParamCount}},{{end}} {{.SyscallParamList}}){{end}}
 
 {{define "tmpvarsreadback"}}{{range .Params}}{{if .TmpVarReadbackCode}}
 {{.TmpVarReadbackCode}}{{end}}{{end}}{{end}}