Update buildcpp.py

Author: HONGJICAI

buildcpp.py

@@ -9,5 +9,6 @@
         code += f.readlines()
     with open("a.cpp", "w") as f:
         f.writelines(code)
-    cmd = "g++ a.cpp -std=c++20"
-    os.system(cmd)
+    cmd = "g++ a.cpp -std=c++11"
+    if 0 != os.system(cmd):
+        exit(-1)