Update TypeAliases.swift

Author: drspoton

Sources/AttributedStringBuilder/TypeAliases.swift

@@ -8,10 +8,14 @@ import UIKit
 typealias Color = UIColor
 typealias Font = UIFont
 
-#else
+#elseif canImport(AppKit)
 
 import AppKit
 typealias Color = NSColor
 typealias Font = NSFont
 
+#else
+
+#error("wtf")
+
 #endif