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...).

lib/model/requests_test.go

@@ -12,13 +12,13 @@ import (
 	"errors"
 	"os"
 	"path/filepath"
-	"runtime"
 	"strconv"
 	"strings"
 	"sync"
 	"testing"
 	"time"
 
+	"github.com/syncthing/syncthing/lib/build"
 	"github.com/syncthing/syncthing/lib/config"
 	"github.com/syncthing/syncthing/lib/events"
 	"github.com/syncthing/syncthing/lib/fs"
@@ -72,7 +72,7 @@ func TestRequestSimple(t *testing.T) {
 func TestSymlinkTraversalRead(t *testing.T) {
 	// Verify that a symlink can not be traversed for reading.
 
-	if runtime.GOOS == "windows" {
+	if build.IsWindows {
 		t.Skip("no symlink support on CI")
 		return
 	}
@@ -115,7 +115,7 @@ func TestSymlinkTraversalRead(t *testing.T) {
 func TestSymlinkTraversalWrite(t *testing.T) {
 	// Verify that a symlink can not be traversed for writing.
 
-	if runtime.GOOS == "windows" {
+	if build.IsWindows {
 		t.Skip("no symlink support on CI")
 		return
 	}
@@ -214,7 +214,7 @@ func TestRequestCreateTmpSymlink(t *testing.T) {
 }
 
 func TestRequestVersioningSymlinkAttack(t *testing.T) {
-	if runtime.GOOS == "windows" {
+	if build.IsWindows {
 		t.Skip("no symlink support on Windows")
 	}
 
@@ -613,7 +613,7 @@ func TestParentDeletion(t *testing.T) {
 // TestRequestSymlinkWindows checks that symlinks aren't marked as deleted on windows
 // Issue: https://github.com/syncthing/syncthing/issues/5125
 func TestRequestSymlinkWindows(t *testing.T) {
-	if runtime.GOOS != "windows" {
+	if !build.IsWindows {
 		t.Skip("windows specific test")
 	}