Fix the build of spawn on windows after the syslog changes

I forgot syslog doesn't exist on windows. Now we're providing a nil
io.WriteCloser to get code using flags.Syslog to compile at least. I
might have to change it to an interface or switch to a different syslog
library that supports remote syslogging on any platform (or write that
myself I think it's just a socket with text).

spawn/embedspawn/logs_handler.go

@@ -110,7 +110,7 @@ func (h *logHandler) HandleLogs(logs io.ReadCloser, tag string) {
 		//
 		// It's only syslog that misses it because spawn doesn't normally syslog for
 		// children, they syslog on their own.
-		flags.Syslog.Info(panicLog)
+		io.WriteString(flags.Syslog, panicLog)
 	}
 }
 

spawn/embedspawn/spawn.go

@@ -8,6 +8,7 @@ import (
 	"errors"
 	"flag"
 	"fmt"
+	"io"
 	"io/fs"
 	"log"
 	"os"
@@ -89,7 +90,7 @@ func Run(flagset *flag.FlagSet, args []string) {
 				panicOut.WriteString(" panic: ")
 				fmt.Fprint(&panicOut, value, "\n\n")
 				panicOut.Write(debug.Stack())
-				flags.Syslog.Info(panicOut.String())
+				io.WriteString(flags.Syslog, panicOut.String())
 			}
 			panic(value)
 		}

tools/flags/syslog_flag.go

@@ -19,6 +19,9 @@ import (
 // initialized if the -syslog or the -syslog_remote flag is set and [flag.Parse]
 // has been called.
 //
+// If you need to compile your code on windows you can only assume
+// io.WriteCloser.
+//
 // Using this writer directly will not also log to stdout
 var Syslog *syslog.Writer
 

tools/flags/syslog_flag_nil.go

@@ -0,0 +1,10 @@
+//go:build nosyslog || windows
+
+package flags
+
+import "io"
+
+// This is provided so that we can still compile on windows and if people use
+// -nosyslog, since flags.Syslog is a public API.
+
+var Syslog io.WriteCloser = nil