Add feature test macro _ISOC2Y_SOURCE

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>

1 files changed, 7 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 2fe0396b2d..1d048de0e6 100644
--- a/NEWS
+++ b/NEWS
@@ -31,6 +31,13 @@ Major new features:
 * The iconv program now supports converting files in place.  The program
   automatically uses a temporary file if required.
 
+* The GNU C Library now supports a feature test macro _ISOC2Y_SOURCE to
+  enable features from the draft ISO C2Y standard.  Only some features from
+  this draft standard are supported by the GNU C Library, and as the draft
+  is under active development, the set of features enabled by this macro is
+  liable to change.  Features from C2Y are also enabled by _GNU_SOURCE, or
+  by compiling with "gcc -std=gnu2y".
+
 Deprecated and removed features, and other changes affecting compatibility:
 
 * The big-endian ARC port (arceb-linux-gnu) has been removed.