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.

serial_windows.go

@@ -22,6 +22,8 @@ type windowsPort struct {
 	handle syscall.Handle
 }
 
+//go:generate go run extras/mksyscall_windows.go -output syscall_windows.go serial_windows.go
+
 //sys regEnumValue(key syscall.Handle, index uint32, name *uint16, nameLen *uint32, reserved *uint32, class *uint16, value *uint16, valueLen *uint32) (regerrno error) = advapi32.RegEnumValueW
 
 func nativeGetPortsList() ([]string, error) {