Comment 7 for bug 1783706

Confirming, we've used this change (_IO_ftrylockfile replaced by _IO_EOF_SEEN) in other packages that FTBFS with the new toolchain.

Please also make sure _IO_IN_BACKUP is defined (to 0x100) if it's being used.

cf. similar changes in coreutils:

Index: coreutils-8.28/lib/fseterr.c
===================================================================
--- coreutils-8.28.orig/lib/fseterr.c
+++ coreutils-8.28/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 */
Index: coreutils-8.28/lib/stdio-impl.h
===================================================================
--- coreutils-8.28.orig/lib/stdio-impl.h
+++ coreutils-8.28/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. */