Add test case

Author: DougGregor

test/SILGen/distributed_thunk.swift

@@ -0,0 +1,19 @@
+// RUN:  %target-swift-emit-silgen %s -enable-experimental-distributed -disable-availability-checking | %FileCheck %s --dump-input=fail
+// REQUIRES: concurrency
+// REQUIRES: distributed
+
+import _Distributed
+
+distributed actor DA { }
+
+extension DA {
+  // CHECK-LABEL: sil hidden [thunk] [ossa] @$s17distributed_thunk2DAC1fyyFTd : $@convention(method) @async (@guaranteed DA) -> @error Error
+  // CHECK: function_ref @swift_distributed_actor_is_remote
+
+  // Call the actor function
+  // CHECK: function_ref @$s17distributed_thunk2DAC1fyyF : $@convention(method) (@guaranteed DA) -> ()
+
+  // ... or the remote thunk
+  // CHECK: dynamic_function_ref @$s17distributed_thunk2DAC9_remote_fyyYaKF : $@convention(method) @async (@guaranteed DA) -> @error Error
+  distributed func f() { }
+}