cmd/vet: make TestTags pass on windows

Update golang/go#11811

Change-Id: I3d875acf58a015fa4cae16473a118ac8196b9b44
Reviewed-on: https://go-review.googlesource.com/12789
Reviewed-by: Andrew Gerrand <adg@golang.org>

cmd/vet/vet_test.go

@@ -15,7 +15,7 @@ import (
 
 const (
 	dataDir = "testdata"
-	binary  = "testvet"
+	binary  = "testvet.exe"
 )
 
 // Run this shell script, but do it in Go so it can be run by "go test".
@@ -93,10 +93,10 @@ func TestTags(t *testing.T) {
 		t.Fatal(err)
 	}
 	// file1 has testtag and file2 has !testtag.
-	if !bytes.Contains(output, []byte("tagtest/file1.go")) {
+	if !bytes.Contains(output, []byte(filepath.Join("tagtest", "file1.go"))) {
 		t.Error("file1 was excluded, should be included")
 	}
-	if bytes.Contains(output, []byte("tagtest/file2.go")) {
+	if bytes.Contains(output, []byte(filepath.Join("tagtest", "file2.go"))) {
 		t.Error("file2 was included, should be excluded")
 	}
 }