lib/52529: C11 stdatomic.h missing

[Thomas Klausner <wiz%NetBSD.org@localhost>]

>Number:         52529
>Category:       lib
>Synopsis:       C11 stdatomic.h missing
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Sep 06 13:40:00 +0000 2017
>Originator:     Thomas Klausner
>Release:        NetBSD 8.99.2
>Organization:
Curiosity is the very basis of education and if you tell me that 
curiosity killed the cat, I say only that the cat died nobly.
- Arnold Edinborough
>Environment:
Architecture: x86_64
Machine: amd64
>Description:
NetBSD does not provide the stdatomic.h header which is specified by C11.

Some software would like to use it, like gnutls.
>How-To-Repeat:
less /usr/include/stdatomic.h
>Fix:
FreeBSD has one, see e.g.
https://github.com/freebsd/freebsd/blob/master/sys/sys/stdatomic.h