stdio: Remove the usage of $(fno-unit-at-a-time) for errlist.c

The errlist.c is built with -fno-toplevel-reorder to avoid compiler to
reorder the compat assembly directives due an assembler issue [1]
(fixed on 2.39).

This patch removes the compiler flags by split the compat symbol
generation in two phases.  First the _sys_errlist_internal internal
without any compat symbol directive is preprocessed to generate an
assembly source code.  This generate assembly is then used as input
on a platform agnostic errlist-data.S which then creates the compat
definitions.  This prevents compiler to move any compat directive
prior the _sys_errlist_internal definition itself.

Checked on a make check run-built-tests=no on all affected ABIs.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=29012

stdio-common/err_map.h

@@ -0,0 +1,24 @@
+/* Internal errno names mapping definition.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _ERR_MAP_H
+#define _ERR_MAP_H
+
+#define ERR_MAP(n) (n)
+
+#endif