[test] Mark availability on failing validation-tests

The validation-test suite was incorrectly being run without the
concurrency feature enabled, so the tests were disabled. Now that
they're running, they need fixed availability annotations.

Author: porglezomp

validation-test/compiler_crashers_2_fixed/rdar70144083.swift

@@ -2,6 +2,7 @@
 
 // REQUIRES: concurrency
 
+@available(SwiftStdlib 5.5, *)
 public protocol AsyncIteratorProtocol {
     associatedtype Element
     associatedtype Failure: Error
@@ -10,6 +11,7 @@ public protocol AsyncIteratorProtocol {
     mutating func cancel()
 }
 
+@available(SwiftStdlib 5.5, *)
 public protocol AsyncSequence {
     associatedtype Element
     associatedtype Failure: Error
@@ -18,6 +20,7 @@ public protocol AsyncSequence {
     func makeAsyncIterator() -> AsyncIterator
 }
 
+@available(SwiftStdlib 5.5, *)
 struct Just<Element>: AsyncSequence {
     typealias Failure = Never
 

validation-test/compiler_crashers_2_fixed/rdar71260862.swift

@@ -1,6 +1,7 @@
 // RUN: %target-swift-frontend %s -emit-ir -enable-library-evolution -enable-experimental-concurrency
 // REQUIRES: concurrency
 
+@available(SwiftStdlib 5.5, *)
 public class X {
   public func f() async { }
 }

validation-test/compiler_crashers_2_fixed/rdar71491604.swift

@@ -1,6 +1,7 @@
 // RUN: %target-swift-frontend %s -emit-ir -enable-library-evolution -enable-experimental-concurrency
 // REQUIRES: concurrency
 
+@available(SwiftStdlib 5.5, *)
 public protocol P {
   func f() async
 }

validation-test/compiler_crashers_2_fixed/rdar71816041.swift

@@ -1,8 +1,10 @@
 // RUN: %target-swift-frontend -emit-ir -primary-file %s -enable-experimental-concurrency
 // REQUIRES: concurrency
 
+@available(SwiftStdlib 5.5, *)
 func getIntAndString() async -> (Int, String) { (5, "1") }
 
+@available(SwiftStdlib 5.5, *)
 func testDecompose() async -> Int {
   async let (i, s) = await getIntAndString()
   return await i

validation-test/compiler_crashers_2_fixed/rdar72397303.swift

@@ -1,11 +1,14 @@
 // RUN: %target-swift-frontend %s -emit-ir -enable-experimental-concurrency
 // REQUIRES: concurrency
 
+@available(SwiftStdlib 5.5, *)
 protocol P {
   func f<T>() async throws -> T?
 }
+@available(SwiftStdlib 5.5, *)
 extension P {
   func f<T>() async throws -> T? { nil }
 }
+@available(SwiftStdlib 5.5, *)
 class X: P {}
 

validation-test/compiler_crashers_2_fixed/sr15248.swift

@@ -1,5 +1,6 @@
 // RUN: %target-swift-frontend -emit-ir %s
 // REQUIRES: concurrency
+
 private struct TransformResult<T> {
     var index: Int
     var transformedElement: T
@@ -11,7 +12,7 @@ private struct TransformResult<T> {
 }
 
 public extension Collection {
-    @available(macOS 12.0.0, *)
+    @available(SwiftStdlib 5.5, *)
     private func f<T>(_ transform: @escaping (Element) async throws -> T) async throws -> [T] {
         return try await withThrowingTaskGroup(of: TransformResult<T>.self) { group in
           return []