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/errlist.c

@@ -16,29 +16,17 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <stdio.h>
+#include <array_length.h>
+#include <err_map.h>
 #include <errno.h>
 #include <libintl.h>
-#include <array_length.h>
-
-#ifndef ERR_MAP
-# define ERR_MAP(n) n
-#endif
-
-const char *const _sys_errlist_internal[] =
-  {
-#define _S(n, str)         [ERR_MAP(n)] = str,
-#include <errlist.h>
-#undef _S
-  };
+#include <stdio.h>
 
 const char *
 __get_errlist (int errnum)
 {
   int mapped = ERR_MAP (errnum);
-  if (mapped >= 0 && mapped < array_length (_sys_errlist_internal))
+  if (mapped >= 0 && mapped < _sys_errlist_internal_len)
     return _sys_errlist_internal[mapped];
   return NULL;
 }
-
-#include <errlist-compat.c>