* libc/posix/readdir_r.c: Fix potential read past dirp->dd_buf.
	* acconfig.h (_UNBUF_STREAM_OPT): Undefine.
	* newlib.hin (_UNBUF_STREAM_OPT): Undefine.
	* configure.in (--enable-newlib-unbuf-stream-opt): New option.
	* configure: Regenerate.
	* libc/stdio/vfprintf.c (_VFPRINTF_R): Don't do optimization on
	unbuffered stream files.
	* libc/stdio/vfwprintf.c (_VFWPRINTF_R): Likewise.
	* README: Add description about the option.
	* newlib.hin (_UNBUF_STREAM_OPT): Undefine.
	* configure.in (--enable-newlib-unbuf-stream-opt): New option.
	* configure: Regenerate.
	* libc/stdio/vfprintf.c (_VFPRINTF_R): Don't do optimization on
	unbuffered stream files.
	* libc/stdio/vfwprintf.c (_VFWPRINTF_R): Likewise.
	* README: Add description about the option.