libstdc++: Fix up submdspan std exports

libstdc++: Fix up submdspan std exports

On Mon, Feb 16, 2026 at 01:34:50PM +0100, Tomasz Kamiński wrote:
> This patch implements LWG 4491, addressing C++26 NB comments.
>
> libstdc++-v3/ChangeLog:
>
>       * include/std/mdspan (std::submdspan_extents): Rename to...
>       (std::subextents): Rename of submdspan_extents.
>       (std::submdspan_canonicalize_slices): Rename to...
>       (std::canonical_slices):

This broke
+FAIL: g++.dg/modules/compile-std1.C -std=c++26 (test for excess errors)
+FAIL: g++.dg/modules/compile-std1.C module-cmi std (gcm.cache/std.gcm)
+FAIL: g++.dg/modules/compile-std1.C module-cmi std.compat (gcm.cache/std.compat.gcm)
on all targets.

The following patch fixes it.

2026-02-17  Jakub Jelinek  <jakub@redhat.com>

	* src/c++23/std.cc.in (std::submdspan_canonicalize_slices,
	std::submdspan_extents): Remove exports.
	(std::canonical_slices, std::subextents): New exports.