* include/features.h (_POSIX_C_SOURCE): Document the value of 202405L
for POSIX.1-2024.  Set it to 202405L when _GNU_SOURCE or _DEFAULT_SOURCE
is defined.
(_XOPEN_SOURCE): Document the value of 800 for POSIX-1.2024.  Set it to
800 when _GNU_SOURCE is defined.
(__USE_XOPEN2K24, __USE_XOPEN2K24XSI): New internal macros.  Set them
when _POSIX_C_SOURCE is 202405L or greater and/or when _XOPEN_SOURCE is
800 or greater.
* manual/creature.texi (Feature Test Macros): Document the new values
for _POSIX_C_SOURCE and _XOPEN_SOURCE.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Signed-off-by: Collin Funk <collin.funk1@gmail.com>

clang does not allow to redefine attributes after function declaration.
Although it work for external usage, its breaks the build for internal
symbol that glibc provides as optimization (for instance bsearch
with stdlib-bsearch.h or __cmsg_nxthdr).

Disable such optimization for clang while building glibc.

Reviewed-by: Sam James <sam@gentoo.org>

Signed-off-by: Andreas K. Hüttel <dilfridge@gentoo.org>

Signed-off-by: Andreas K. Hüttel <dilfridge@gentoo.org>

This patch starts preparation for C2Y support in glibc headers by
adding a feature test macro _ISOC2Y_SOURCE and corresponding
__GLIBC_USE (ISOC2Y). (I mostly copied the work of Joseph Myers
for C2X). As with other such macros, C2Y features are also
enabled by compiling for a standard newer than C23, or by using
_GNU_SOURCE.

This patch does not itself enable anything new in the headers for C2Y;
that is to be done in followup patches. (For example an implementation
of WG14 N3349.)

Once C2Y becomes an actual standard we'll presumably move to using the
actual year in the feature test macro and __GLIBC_USE, with some
period when both macro spellings are accepted, as was done with
_ISOC2X_SOURCE.

Tested for x86_64.

Signed-off-by: Lenard Mollenkopf <glibc@lenardmollenkopf.de>

Signed-off-by: Andreas K. Hüttel <dilfridge@gentoo.org>

WG14 decided to use the name C23 as the informal name of the next
revision of the C standard (notwithstanding the publication date in
2024).  Update references to C2X in glibc to use the C23 name.

This is intended to update everything *except* where it involves
renaming files (the changes involving renaming tests are intended to
be done separately).  In the case of the _ISOC2X_SOURCE feature test
macro - the only user-visible interface involved - support for that
macro is kept for backwards compatibility, while adding
_ISOC23_SOURCE.

Tested for x86_64.

Signed-off-by: Andreas K. Hüttel <dilfridge@gentoo.org>