New module 'poll-h'. * lib/poll.in.h: Include c++defs.h and warn-on-use.h. (poll): Use modern idiom. * modules/poll-h: New file. * modules/poll (Files): Remove lib/poll.in.h. (Depends-on): Add poll-h. (configure.ac): Invoke gl_POLL_MODULE_INDICATOR. (Makefile.am): Move code for generation of poll.h to modules/poll-h. * m4/poll_h.m4: New file. * m4/poll.m4 (gl_FUNC_POLL): Require gl_POLL_H. Don't check for poll.h here. Don't set POLL_H here. Instead, set HAVE_POLL and REPLACE_POLL and invoke gl_REPLACE_POLL_H. * lib/poll.c: Use common idiom. * tests/test-poll.c: Likewise. * doc/posix-headers/poll.texi: Mention the poll-h module. Suggested by Eric Blake.