* lib/stdio_.h [REPLACE_FFLUSH]: Declare rpl_fflush. * modules/stdio (Makefile.am): Support fflush. * m4/stdio_h.m4 (gl_STDIO_H_DEFAULTS): Likewise. * modules/fflush: New file. * lib/fflush.c: Likewise. * m4/fflush.m4: Likewise. * modules/fflush-tests: New test. * tests/test-fflush.c: Likewise. * MODULES.html.sh (Input/output <stdio.h>): Document new module.