disable availability checking for async test

Author: WANGJIEKE

test/Interop/SwiftToCxx/functions/swift-no-expose-unsupported-async-func.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend %s -typecheck -module-name Functions -clang-header-expose-public-decls -emit-clang-header-path %t/functions.h
+// RUN: %target-swift-frontend %s -typecheck -module-name Functions -disable-availability-checking -clang-header-expose-public-decls -emit-clang-header-path %t/functions.h
 // RUN: %FileCheck %s < %t/functions.h
 
 // RUN: %check-interop-cxx-header-in-clang(%t/functions.h)