Use go:generate to create syscall_windows.go

This dramatically improves maintainability of generated files.

This will be eventually implemented on other generated files as well.

syscall_windows.go

@@ -1,18 +1,19 @@
-// go build mksyscall_windows.go && ./mksyscall_windows serial_windows.go
-// MACHINE GENERATED BY THE COMMAND ABOVE; DO NOT EDIT
+// MACHINE GENERATED BY 'go generate' COMMAND; DO NOT EDIT
 
 package serial
 
 import (
 	"syscall"
 	"unsafe"
+
+	"golang.org/x/sys/windows"
 )
 
 var _ unsafe.Pointer
 
 var (
-	modadvapi32 = syscall.NewLazyDLL("advapi32.dll")
-	modkernel32 = syscall.NewLazyDLL("kernel32.dll")
+	modadvapi32 = windows.NewLazySystemDLL("advapi32.dll")
+	modkernel32 = windows.NewLazySystemDLL("kernel32.dll")
 
 	procRegEnumValueW   = modadvapi32.NewProc("RegEnumValueW")
 	procGetCommState    = modkernel32.NewProc("GetCommState")