macos: clang: set to cxx11 standard avoid 'auto' not allowed issues

- https://forum.d2learn.org/topic/119

Signed-off-by: sunrisepeak <speakshen@163.com>

Author: Sunrisepeak

dslings/xmake.lua

@@ -5,6 +5,7 @@ if is_host("windows") then
 end
 
 target("00-0-hello-mcpp")
+    set_languages("cxx11")
     add_files("hello-mcpp.cpp")
 
 includes("cpp11")