stdio: Split __get_errname definition from errlist.c

The loader does not need to pull all __get_errlist definitions
and its size is decreased:

Before:
$ size elf/ld.so
   text    data     bss     dec     hex filename
 197774   11024     456  209254   33166 elf/ld.so

After:
$ size elf/ld.so
   text    data     bss     dec     hex filename
 191510    9936     456  201902   314ae elf/ld.so

Checked on x86_64-linux-gnu.

1 files changed, 61 insertions, 0 deletions

diff --git a/stdio-common/errname.c b/stdio-common/errname.c
new file mode 100644
index 0000000000..08e4cecbd1
--- /dev/null
+++ b/stdio-common/errname.c
@@ -0,0 +1,61 @@
+/* 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/>.  */
+
+#include <stdio.h>
+#include <errno.h>
+#include <libintl.h>
+#include <array_length.h>
+
+#ifndef ERR_MAP
+# define ERR_MAP(n) n
+#endif
+
+static const union sys_errname_t
+{
+  struct
+  {
+#define MSGSTRFIELD1(line) str##line
+#define MSGSTRFIELD(line)  MSGSTRFIELD1(line)
+#define _S(n, str)         char MSGSTRFIELD(__LINE__)[sizeof(#n)];
+#include <errlist.h>
+#undef _S
+  };
+  char str[0];
+} _sys_errname = { {
+#define _S(n, s) #n,
+#include <errlist.h>
+#undef _S
+} };
+
+static const unsigned short _sys_errnameidx[] =
+{
+#define _S(n, s) \
+  [ERR_MAP(n)] = offsetof(union sys_errname_t, MSGSTRFIELD(__LINE__)),
+#include <errlist.h>
+#undef _S
+};
+
+const char *
+__get_errname (int errnum)
+{
+  int mapped = ERR_MAP (errnum);
+  if (mapped < 0 || mapped >= array_length (_sys_errnameidx)
+      || (mapped > 0 && _sys_errnameidx[mapped] == 0))
+    return NULL;
+  return _sys_errname.str + _sys_errnameidx[mapped];
+}