[nfc] Add a test for the attribute fix-its.

Author: zoecarver

test/Interop/Cxx/class/fixit-add-safe-to-import-self-contained.swift

@@ -0,0 +1,41 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: not %target-swift-frontend -typecheck -I %t/Inputs  %t/test.swift  -enable-experimental-cxx-interop 2>&1 | %FileCheck %s
+
+//--- Inputs/module.modulemap
+module Test {
+    header "test.h"
+    requires cplusplus
+}
+
+//--- Inputs/test.h
+struct Ptr { int *p; };
+
+struct X {
+  int *test() { }
+  Ptr other() { }
+};
+
+//--- test.swift
+
+import Test
+
+public func test(x: X) {
+  // CHECK: note: Mark method 'test' as 'safe_to_import' in C++ to make it available in Swift.
+  // CHECK: int *test() { }
+  // CHECK: ^
+  // CHECK: __attribute__((swift_attr("safe_to_import")))
+  
+  x.test()
+  
+  // CHECK: note: Mark method 'other' as 'safe_to_import' in C++ to make it available in Swift.
+  // CHECK: Ptr other() { }
+  // CHECK: ^
+  // CHECK: __attribute__((swift_attr("safe_to_import")))
+  
+  // CHECK: note: Mark type 'Ptr' as 'self_contained' in C++ to make methods that use it available in Swift.
+  // CHECK: struct X {
+  // CHECK: ^
+  // CHECK: __attribute__((swift_attr("self_contained")))
+  x.other()
+}