Test predatesConcurrency is only applied in Swift 5

Ensure that the predates concurrency behavior is only applied for Swift
5 and not for Swift 6.

Author: etcwilde

test/Concurrency/toplevel/Inputs/foo.swift

@@ -0,0 +1,3 @@
+func foo() -> Int {
+    a + 10
+}

test/Concurrency/toplevel/main.swift

@@ -0,0 +1,40 @@
+// RUN: not %target-swift-frontend -enable-experimental-async-top-level -swift-version 6 -typecheck %s %S/Inputs/foo.swift 2>&1 | %FileCheck %s --check-prefixes='Swift6-CHECK,CHECK'
+// RUN: not %target-swift-frontend -enable-experimental-async-top-level -swift-version 5 -typecheck %s %S/Inputs/foo.swift 2>&1 | %FileCheck %s --check-prefixes='Swift5-CHECK,CHECK'
+
+var a = 10
+
+func nonIsolatedSynchronous() {
+    print(a)
+// Swift6-CHECK: var 'a' isolated to global actor 'MainActor'
+// Swift6-CHECK: add '@MainActor' to make global function 'nonIsolatedSynchronous()' part of global actor 'MainActor'
+
+// Swift5-CHECK-NOT: var 'a' isolated to global actor 'MainActor'
+// Swift5-CHECK-NOT: add '@MainActor' to make global function 'nonIsolatedSynchronous()' part of global actor 'MainActor'
+}
+
+func nonIsolatedAsync() async {
+    print(a)
+// CHECK: expression is 'async' but is not marked with 'await'
+// CHECK: property access is 'async'
+}
+
+await nonIsolatedAsync()
+
+// Swift6-CHECK: foo.swift{{.*}}var 'a' isolated to global actor 'MainActor' can not be referenced from this synchronous context
+// Swift6-CHECK: foo.swift{{.*}}add '@MainActor' to make global function 'foo()' part of global actor 'MainActor'
+// Swift6-CHECK: var declared here
+
+// Swift5-CHECK-NOT: foo.swift{{.*}}var 'a' isolated to global actor 'MainActor' can not be referenced from this synchronous context
+// Swift5-CHECK-NOT: foo.swift{{.*}}add '@MainActor' to make global function 'foo()' part of global actor 'MainActor'
+// Swift5-CHECK-NOT: var declared here
+
+@MainActor
+func isolated() {
+    print(a)
+}
+
+func asyncFun() async {
+    await print(a)
+}
+
+await asyncFun()