Fix compilation with gcc-8.2.0.
https://bugs.gentoo.org/681904

--- emacs-23.4-orig/src/s/gnu-linux.h
+++ emacs-23.4/src/s/gnu-linux.h
@@ -150,7 +150,8 @@
 
 #ifdef emacs
 #include <stdio.h>  /* Get the definition of _IO_STDIO_H.  */
-#if defined(_IO_STDIO_H) || defined(_STDIO_USES_IOSTREAM)
+#if defined(_IO_STDIO_H) || defined(_STDIO_USES_IOSTREAM) \
+    || defined _IO_EOF_SEEN || __GNU_LIBRARY__ == 1
 /* new C libio names */
 #define GNU_LIBRARY_PENDING_OUTPUT_COUNT(FILE) \
   ((FILE)->_IO_write_ptr - (FILE)->_IO_write_base)