Remove GNU_LIBRARY_PENDING_OUTPUT_COUNT

Remove GNU_LIBRARY_PENDING_OUTPUT_COUNT

* configure.ac (GNU_LIBRARY_PENDING_OUTPUT_COUNT): Remove.
(PENDING_OUTPUT_COUNT): Absorb GNU_LIBRARY_PENDING_OUTPUT_COUNT.
(DISPNEW_NEEDS_STDIO_EXT): New define.

* src/dispnew.c (GNU_LIBRARY_PENDING_OUTPUT_COUNT, PENDING_OUTPUT_COUNT):
Let configure handle it.
(stdio_ext.h) [DISPNEW_NEEDS_STDIO_EXT]: Include it.

* nt/config.nt (GNU_LIBRARY_PENDING_OUTPUT_COUNT): Remove.
(PENDING_OUTPUT_COUNT): Define it as dispnew.c used to.

* admin/CPP-DEFINES (GNU_LIBRARY_PENDING_OUTPUT_COUNT): Remove.