build: Generalize code signing

Should, at the least, also codesign when building zip for mac.

build.go

@@ -489,10 +489,7 @@ func buildTar(target target) {
 	}
 
 	build(target, tags)
-
-	if goos == "darwin" {
-		macosCodesign(target.BinaryName())
-	}
+	codesign(target)
 
 	for i := range target.archiveFiles {
 		target.archiveFiles[i].src = strings.Replace(target.archiveFiles[i].src, "{{binary}}", target.BinaryName(), 1)
@@ -515,10 +512,7 @@ func buildZip(target target) {
 	}
 
 	build(target, tags)
-
-	if goos == "windows" {
-		windowsCodesign(target.BinaryName())
-	}
+	codesign(target)
 
 	for i := range target.archiveFiles {
 		target.archiveFiles[i].src = strings.Replace(target.archiveFiles[i].src, "{{binary}}", target.BinaryName(), 1)
@@ -1179,6 +1173,15 @@ func zipFile(out string, files []archiveFile) {
 	}
 }
 
+func codesign(target target) {
+	switch goos {
+	case "windows":
+		windowsCodesign(target.BinaryName())
+	case "darwin":
+		macosCodesign(target.BinaryName())
+	}
+}
+
 func macosCodesign(file string) {
 	if pass := os.Getenv("CODESIGN_KEYCHAIN_PASS"); pass != "" {
 		bs, err := runError("security", "unlock-keychain", "-p", pass)