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/model_test.go

@@ -15,7 +15,6 @@ import (
 	"math/rand"
 	"os"
 	"path/filepath"
-	"runtime"
 	"runtime/pprof"
 	"sort"
 	"strconv"
@@ -26,6 +25,7 @@ import (
 	"time"
 
 	"github.com/pkg/errors"
+	"github.com/syncthing/syncthing/lib/build"
 	"github.com/syncthing/syncthing/lib/config"
 	"github.com/syncthing/syncthing/lib/db"
 	"github.com/syncthing/syncthing/lib/db/backend"
@@ -1463,7 +1463,7 @@ func changeIgnores(t *testing.T, m *testModel, expected []string) {
 		t.Errorf("Incorrect ignores: %v != %v", ignores2, ignores)
 	}
 
-	if runtime.GOOS == "darwin" {
+	if build.IsDarwin {
 		// see above
 		time.Sleep(time.Second)
 	} else {
@@ -2130,7 +2130,7 @@ func TestIssue4357(t *testing.T) {
 func TestIssue2782(t *testing.T) {
 	// CheckHealth should accept a symlinked folder, when using tilde-expanded path.
 
-	if runtime.GOOS == "windows" {
+	if build.IsWindows {
 		t.Skip("not reliable on Windows")
 		return
 	}
@@ -2471,7 +2471,7 @@ func TestNoRequestsFromPausedDevices(t *testing.T) {
 
 // TestIssue2571 tests replacing a directory with content with a symlink
 func TestIssue2571(t *testing.T) {
-	if runtime.GOOS == "windows" {
+	if build.IsWindows {
 		t.Skip("Scanning symlinks isn't supported on windows")
 	}
 
@@ -2510,7 +2510,7 @@ func TestIssue2571(t *testing.T) {
 
 // TestIssue4573 tests that contents of an unavailable dir aren't marked deleted
 func TestIssue4573(t *testing.T) {
-	if runtime.GOOS == "windows" {
+	if build.IsWindows {
 		t.Skip("Can't make the dir inaccessible on windows")
 	}
 
@@ -2802,7 +2802,7 @@ func TestVersionRestore(t *testing.T) {
 		"dir/file.txt",
 		"dir/existing.txt",
 	} {
-		if runtime.GOOS == "windows" {
+		if build.IsWindows {
 			file = filepath.FromSlash(file)
 		}
 		dir := filepath.Dir(file)
@@ -2886,7 +2886,7 @@ func TestVersionRestore(t *testing.T) {
 
 	// Check that content of files matches to the version they've been restored.
 	for file, version := range restore {
-		if runtime.GOOS == "windows" {
+		if build.IsWindows {
 			file = filepath.FromSlash(file)
 		}
 		tag := version.In(time.Local).Truncate(time.Second).Format(versioner.TimeFormat)
@@ -2918,7 +2918,7 @@ func TestVersionRestore(t *testing.T) {
 	must(t, err)
 	for file, versions := range allFileVersions {
 		key := file
-		if runtime.GOOS == "windows" {
+		if build.IsWindows {
 			file = filepath.FromSlash(file)
 		}
 		for _, version := range versions {