mac 下 使用 gcc5.2.0 ,编译报错 无法识别 __has_feature

今天尝试在mac 上使用g++5，通过brew 可以轻松安装，但是在编译一个简单的程序时报错：

In file included from /usr/include/wchar.h:72:0,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/cwchar:44,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/bits/postypes.h:40,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/iosfwd:40,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/ios:38,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/ostream:38,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/iostream:39,

                 from easyTest.cpp:1:

/usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/Availability.h:179:44: error: missing binary operator before token "("

 #if defined(__has_feature) && __has_feature(attribute_availability_with_message)

                                            ^

In file included from /usr/include/wchar.h:72:0,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/cwchar:44,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/bits/postypes.h:40,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/iosfwd:40,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/ios:38,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/ostream:38,

                 from /usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/iostream:39,

                 from easyTest.cpp:1:

/usr/local/Cellar/gcc5/5.2.0/include/c++/5.2.0/Availability.h:189:44: error: missing binary operator before token "("

 #if defined(__has_feature) && __has_feature(attribute_availability_app_extension)

                                            ^

make: *** [easyTest] Error 1

应该是gcc安装有问题，尝试从源码安装 ，但是每次编译不过，
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通过原理来看，需要在gcc自己使用的头文件中将 __has_feature 定义，但是又不能影响系统头文件，目前简单的解决方式是：
将 availability.h 拷贝套gcc5的安装目录一份，在gcc5 进行编译的时候会优先查找这个目录下的头文件，也符合修改编译源码时候 fixincludes.def的目标。

?  5.2.0 git:(master)  diff Availability.h /usr/include/Availability.h 

173,177d172

< /****

< #ifndef __has_feature

< #define __has_feature(x) 0

< #endif

< *****/