Add regression test for rdar://152700122

Author: slavapestov

test/Availability/operator_availability.swift

@@ -29,3 +29,20 @@ func testAvailability() {
   _ = (1 as Int32) <=< (1 as Int32)   // okay
   _ = (1 as Int32) >=> (1 as Int32)   // expected-error{{'>=>' is unavailable}}
 }
+
+// rdar://problem/152700122
+infix operator ~>
+public func ~><T> (lhs: T, rhs: (T) -> Void) -> T {
+  fatalError()
+}
+
+struct S {
+  @available(macOS 20, *)
+  func f() {}
+}
+
+let s = S() ~> {
+  if #available(macOS 20.0, *) {
+    $0.f()
+  }
+}