[tz] Building tz with gcc-13

[Brian Inglis]

On 2023-03-11 03:18, Martin Jansa via tz wrote:
> I was building tz with gcc-13 and noticed that without explicit -std=c2x it 
> fails to build 2022g version with:
> ```
> zic.c:462:1: warning: ‘noreturn’ attribute ignored [-Wattributes]
>    462 | static ATTRIBUTE_NORETURN void
>        | ^~~~~~
> zic.c:462:27: error: expected identifier or ‘(’ before ‘void’
>    462 | static ATTRIBUTE_NORETURN void
>        |                           ^~~~
> ```
> 
> The last code change on github in this are was:
> https://github.com/eggert/tz/commit/dbfcefe0c129e36e8c5acbcedf1400c1b486d962 
> <https://github.com/eggert/tz/commit/dbfcefe0c129e36e8c5acbcedf1400c1b486d962>
> 
> It builds fine for me with gcc-12 without -std:
> ```
> __STDC_VERSION__ = 201710
> __has_c_attribute(noreturn) = 0
> ```
> and with -std=c2x:
> ```
> __STDC_VERSION__ = 202000
> __has_c_attribute(noreturn) = 0
> __STRICT_ANSI__
> ```
> 
> but with gcc-13 it builds only with explicit -std=c2x:
> ```
> __STDC_VERSION__ = 202000
> __has_c_attribute(noreturn) = 202202
> __STRICT_ANSI__
> ```
> 
> Maybe because __has_c_attribute(noreturn) returns 202202 even when 
> __STDC_VERSION__ doesn't accept it yet?
> ```
> __STDC_VERSION__ = 201710
> __has_c_attribute(noreturn) = 202202
> ```
> 
>  From https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2764.pdf 
> <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2764.pdf> it's not clear to 
> me when exactly [[noreturn]] can be used. It says only this about the value 
> `Drafting note: The value used for __has_c_attribute is a placeholder that is to 
> be replaced by the editors
> with the year and month the proposal is accepted into the working draft.`
> 
> Is it a bug in gcc or should it be handled somehow by private.h?
Does it build with -std=gnu2x - does it relax the order constraints?

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer     but when there is no more to cut
                                 -- Antoine de Saint-Exupéry