lib/60227: dirfd() should be visible and compliant when _POSIX_C_SOURCE is defined

["nia%pkgsrc.org@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60227
>Category:       lib
>Synopsis:       dirfd() should be visible and compliant when _POSIX_C_SOURCE is defined
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon May 04 11:35:01 +0000 2026
>Originator:     nia
>Release:        head, netbsd-11, netbsd-10, netbsd-9...
>Organization:
The NetBSD Foundation
>Environment:
>Description:
Currently dirfd() is unavailable when strict standards mode is enabled
(_POSIX_C_SOURCE). It is defined in POSIX.1-2008:

https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/dirent.h.html

however, our implementation might not be quite compliant, since we
define it as a macro and I don't know whether this is kosher.
>How-To-Repeat:

>Fix: