Add test case for missing musttail in dynamic replacement.

(cherry picked from commit 94593e4)

Author: varungandhi-apple

test/IRGen/async_dynamic_replacement.swift

@@ -0,0 +1,23 @@
+// RUN: %target-swift-frontend %s -emit-ir -disable-objc-interop | %FileCheck %s
+
+// REQUIRES: concurrency
+
+public dynamic func number() async -> Int {
+    return 100
+}
+
+@_dynamicReplacement(for: number())
+internal func _replacement_number() async -> Int {
+    return 200
+}
+
+// rdar://78284346 - Dynamic replacement should use musttail
+//                   for tail calls from swifttailcc to swifttailcc
+// CHECK-LABEL: define {{.*}} swifttailcc void @"$s25async_dynamic_replacement01_C7_numberSiyYaFTI"
+// CHECK-NOT: musttail
+// CHECK: call swifttailcc void
+// CHECK-NEXT: ret void
+
+public func calls_number() async -> Int {
+  await number()
+}