This is a slightly-modified version of Ed's patch from https://gcc.gnu.org/ml/gcc-patches/2015-01/msg02357.html which I plan to commit to CVS tomorrow.
Index: changes.html =================================================================== RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-5/changes.html,v retrieving revision 1.88 diff -u -r1.88 changes.html --- changes.html 10 Mar 2015 17:34:36 -0000 1.88 +++ changes.html 11 Mar 2015 18:06:52 -0000 @@ -189,6 +189,29 @@ of the standard directive <code>#include</code> and the extension <code>#include_next</code> respectively. </li> + <li>A new built-in function to detect the existence of an attribute, + <code>__has_attribute</code>, has been added. The equivalent built-in + function <code>__has_cpp_attribute</code> was added to C++ to support + <a href="http://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations"> + Feature-testing recommendations for C++</a>. + The function <code>__has_attribute</code> is added to all C-like + languages as an extension: +<blockquote><pre> +int +#ifdef __has_attribute +# if __has_attribute(__noinline__) + __attribute__((__noinline__)) +# endif +#endif +foo(int x); +</pre></blockquote> + If an attribute exists a nonzero constant integer is returned. + For standardized C++ attributes a date is returned, otherwise the + constant returned is 1. + The has_attribute macros will add underscores to an attribute name + if necessary to resolve the name. + For C++11 and onwards the attribute may be scoped. + </li> <li>A new set of built-in functions for arithmetics with overflow checking has been added: <code>__builtin_add_overflow</code>, <code>__builtin_sub_overflow</code> and <code>__builtin_mul_overflow</code>