fix build failure against glibc-2.28

https://bugs.gentoo.org/663928

Adopted gnulib's upstream patch:

From 4af4a4a71827c0bc5e0ec67af23edef4f15cee8e Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 5 Mar 2018 10:56:29 -0800
Subject: [PATCH] fflush: adjust to glibc 2.28 libio.h removal
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Problem reported by Daniel P. Berrangé in:
https://lists.gnu.org/r/bug-gnulib/2018-03/msg00000.html
* lib/fflush.c (clear_ungetc_buffer_preserving_position)
(disable_seek_optimization, rpl_fflush):
* lib/fpurge.c (fpurge):
* lib/freadahead.c (freadahead):
* lib/freading.c (freading):
* lib/fseeko.c (fseeko):
* lib/fseterr.c (fseterr):
Check _IO_EOF_SEEN instead of _IO_ftrylockfile.
* lib/stdio-impl.h (_IO_IN_BACKUP) [_IO_EOF_SEEN]:
Define if not already defined.
---
 lib/fflush.c     |  6 +++---
 lib/fpurge.c     |  2 +-
 lib/freading.c   |  2 +-
 lib/fseeko.c     |  4 ++--
 lib/fseterr.c    |  2 +-
 lib/stdio-impl.h |  6 ++++++

--- a/lib/fflush.c
+++ b/lib/fflush.c
@@ -33,7 +33,7 @@
 #undef fflush
 
 
-#if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
+#if defined _IO_EOF_SEEN || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
 
 /* Clear the stream's ungetc buffer, preserving the value of ftello (fp).  */
 static void
@@ -72,7 +72,7 @@ clear_ungetc_buffer (FILE *fp)
 
 #endif
 
-#if ! (defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */)
+#if ! (defined _IO_EOF_SEEN || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */)
 
 # if (defined __sferror || defined __DragonFly__ || defined __ANDROID__) && defined __SNPT
 /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
@@ -148,7 +148,7 @@ rpl_fflush (FILE *stream)
   if (stream == NULL || ! freading (stream))
     return fflush (stream);
 
-#if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
+#if defined _IO_EOF_SEEN || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
 
   clear_ungetc_buffer_preserving_position (stream);
 
--- a/lib/fpurge.c
+++ b/lib/fpurge.c
@@ -62,7 +62,7 @@ fpurge (FILE *fp)
   /* Most systems provide FILE as a struct and the necessary bitmask in
      <stdio.h>, because they need it for implementing getc() and putc() as
      fast macros.  */
-# if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
+# if defined _IO_EOF_SEEN || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
   fp->_IO_read_end = fp->_IO_read_ptr;
   fp->_IO_write_ptr = fp->_IO_write_base;
   /* Avoid memory leak when there is an active ungetc buffer.  */
--- a/lib/freading.c
+++ b/lib/freading.c
@@ -31,7 +31,7 @@ freading (FILE *fp)
   /* Most systems provide FILE as a struct and the necessary bitmask in
      <stdio.h>, because they need it for implementing getc() and putc() as
      fast macros.  */
-# if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
+# if defined _IO_EOF_SEEN || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
   return ((fp->_flags & _IO_NO_WRITES) != 0
           || ((fp->_flags & (_IO_NO_READS | _IO_CURRENTLY_PUTTING)) == 0
               && fp->_IO_read_base != NULL));
--- a/lib/fseeko.c
+++ b/lib/fseeko.c
@@ -47,7 +47,7 @@ fseeko (FILE *fp, off_t offset, int whence)
 #endif
 
   /* These tests are based on fpurge.c.  */
-#if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
+#if defined _IO_EOF_SEEN || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
   if (fp->_IO_read_end == fp->_IO_read_ptr
       && fp->_IO_write_ptr == fp->_IO_write_base
       && fp->_IO_save_base == NULL)
@@ -123,7 +123,7 @@ fseeko (FILE *fp, off_t offset, int whence)
           return -1;
         }
 
-#if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
+#if defined _IO_EOF_SEEN || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
       fp->_flags &= ~_IO_EOF_SEEN;
       fp->_offset = pos;
 #elif defined __sferror || defined __DragonFly__ || defined __ANDROID__
--- a/lib/fseterr.c
+++ b/lib/fseterr.c
@@ -29,7 +29,7 @@ fseterr (FILE *fp)
   /* Most systems provide FILE as a struct and the necessary bitmask in
      <stdio.h>, because they need it for implementing getc() and putc() as
      fast macros.  */
-#if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
+#if defined _IO_EOF_SEEN || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
   fp->_flags |= _IO_ERR_SEEN;
 #elif defined __sferror || defined __DragonFly__ || defined __ANDROID__
   /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
--- a/lib/stdio-impl.h
+++ b/lib/stdio-impl.h
@@ -18,6 +18,12 @@
    the same implementation of stdio extension API, except that some fields
    have different naming conventions, or their access requires some casts.  */
 
+/* Glibc 2.28 made _IO_IN_BACKUP private.  For now, work around this
+   problem by defining it ourselves.  FIXME: Do not rely on glibc
+   internals.  */
+#if !defined _IO_IN_BACKUP && defined _IO_EOF_SEEN
+# define _IO_IN_BACKUP 0x100
+#endif
 
 /* BSD stdio derived implementations.  */
 
-- 
2.19.1