m4: fix building with glibc2.28

srcpkgs/m4/patches/gnulib-freadahead.patch

@@ -0,0 +1,11 @@
+--- lib/freadahead.c
++++ lib/freadahead.c
+@@ -30,7 +30,7 @@ extern size_t __sreadahead (FILE *);
+ size_t
+ freadahead (FILE *fp)
+ {
+-#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_write_ptr > fp->_IO_write_base)
+     return 0;
+   return (fp->_IO_read_end - fp->_IO_read_ptr)

srcpkgs/m4/patches/gnulib-stdio-impl.patch

@@ -0,0 +1,14 @@
+--- lib/stdio-impl.h
++++ 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.  */