all: Add build constants for runtime.GOOS comparisons (#8442)

all: Add package runtimeos for runtime.GOOS comparisons

I grew tired of hand written string comparisons. This adds generated
constants for the GOOS values, and predefined Is$OS constants that can
be iffed on. In a couple of places I rewrote trivial switch:es to if:s,
and added Illumos where we checked for Solaris (because they are
effectively the same, and if we're going to target one of them that
would be Illumos...).

cmd/syncthing/main.go

@@ -199,7 +199,7 @@ func defaultVars() kong.Vars {
 	// Windows, the "default" options.logFile will later be replaced with the
 	// default path, unless the user has manually specified "-" or
 	// something else.
-	if runtime.GOOS == "windows" {
+	if build.IsWindows {
 		vars["logFile"] = "default"
 	} else {
 		vars["logFile"] = "-"

cmd/syncthing/monitor.go

@@ -15,11 +15,11 @@ import (
 	"os/exec"
 	"os/signal"
 	"path/filepath"
-	"runtime"
 	"strings"
 	"syscall"
 	"time"
 
+	"github.com/syncthing/syncthing/lib/build"
 	"github.com/syncthing/syncthing/lib/fs"
 	"github.com/syncthing/syncthing/lib/locations"
 	"github.com/syncthing/syncthing/lib/osutil"
@@ -66,7 +66,7 @@ func monitorMain(options serveOptions) {
 		if err != nil {
 			l.Warnln("Failed to setup logging to file, proceeding with logging to stdout only:", err)
 		} else {
-			if runtime.GOOS == "windows" {
+			if build.IsWindows {
 				// Translate line breaks to Windows standard
 				fileDst = osutil.ReplacingWriter{
 					Writer: fileDst,
@@ -315,7 +315,7 @@ func restartMonitor(args []string) error {
 	// opening the browser on startup.
 	os.Setenv("STRESTART", "yes")
 
-	if runtime.GOOS != "windows" {
+	if !build.IsWindows {
 		// syscall.Exec is the cleanest way to restart on Unixes as it
 		// replaces the current process with the new one, keeping the pid and
 		// controlling terminal and so on

cmd/syncthing/openurl_unix.go

@@ -11,20 +11,18 @@ package main
 
 import (
 	"os/exec"
-	"runtime"
 	"syscall"
+
+	"github.com/syncthing/syncthing/lib/build"
 )
 
 func openURL(url string) error {
-	switch runtime.GOOS {
-	case "darwin":
+	if build.IsDarwin {
 		return exec.Command("open", url).Run()
-
-	default:
-		cmd := exec.Command("xdg-open", url)
-		cmd.SysProcAttr = &syscall.SysProcAttr{
-			Setpgid: true,
-		}
-		return cmd.Run()
 	}
+	cmd := exec.Command("xdg-open", url)
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		Setpgid: true,
+	}
+	return cmd.Run()
 }