improve xcode_emulation.py

test/mac/clang-cxx-language-standard/c++11.cc

Index: test/mac/clang-cxx-language-standard/c++11.cc
diff --git a/test/win/shard/hello4.cc b/test/mac/clang-cxx-language-standard/c++11.cc
similarity index 62%
copy from test/win/shard/hello4.cc
copy to test/mac/clang-cxx-language-standard/c++11.cc
index a94df194999a38e80cde7e2a7205a9f6a39601cd..756dc1c7e6aa4988a18c8870f4151f856d1e547e 100644
--- a/test/win/shard/hello4.cc
+++ b/test/mac/clang-cxx-language-standard/c++11.cc
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-int f4() {
-  return 0;
-}
+static_assert(__cplusplus == 201103L, "wrong c++ standard version");
+
+int main() { return 0; }
+