[wwwdocs] Document __has_attribute in /gcc-5/changes.html

[Jakub Jelinek]

On Wed, Mar 11, 2015 at 06:09:11PM +0000, Jonathan Wakely wrote:
> 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,

Can you please instead write built-in function-like macro?

> +	<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>


	Jakub