(PENDING_OUTPUT_COUNT) [__GNU_LIBRARY__]: Alternate definition for the GNU

C library.  I changed this in version 18 in 1991, but the change never got
propagated.

src/dispnew.c

@@ -52,8 +52,12 @@ the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
 /* Get number of chars of output now in the buffer of a stdio stream.
    This ought to be built in in stdio, but it isn't.
    Some s- files override this because their stdio internals differ.  */
+#ifdef __GNU_LIBRARY__
+#define	PENDING_OUTPUT_COUNT(FILE) ((FILE)->__bufp - (FILE)->__buffer)
+#else
 #define PENDING_OUTPUT_COUNT(FILE) ((FILE)->_ptr - (FILE)->_base)
 #endif
+#endif
 
 /* Nonzero upon entry to redisplay means do not assume anything about
    current contents of actual terminal frame; clear and redraw it.  */