Disable async executables on Linux

Author: natecook1000

Examples/count-lines/CountLines.swift

@@ -9,6 +9,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if os(macOS)
+
 import ArgumentParser
 import Foundation
 
@@ -76,3 +78,13 @@ extension CountLines {
         typealias Command = CountLines
     }
 #endif
+
+#else
+
+@main enum Main {
+    static func main() {
+        print("Unsupported on this platform.")
+    }
+}
+
+#endif

Tools/changelog-authors/ChangelogAuthors.swift

@@ -9,6 +9,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if os(macOS)
+
 import ArgumentParser
 import Foundation
 
@@ -107,3 +109,13 @@ struct ChangelogAuthors: AsyncParsableCommand {
     typealias Command = ChangelogAuthors
   }
 #endif
+
+#else
+
+@main enum Main {
+    static func main() {
+        print("Unsupported on this platform.")
+    }
+}
+
+#endif