* config/os/irix/irix6.5/os_defines.h (_GLIBCXX_FIONREAD_TAKES_OFF_T):
	Define.
	* config/io/basic_file_stdio.cc (__basic_file<char>::showmanyc): Use
	it to decide whether FIONREAD should take an off_t or int argument.

From-SVN: r77336