gnulib-common.m4: Use C2x [[maybe_unused]] when possible.

* m4/gnulib-common.m4 (gl_COMMON_BODY): Define _GL_UNUSED as an alias of
_GL_ATTRIBUTE_MAYBE_UNUSED, not of _GL_ATTRIBUTE_UNUSED.
* lib/binary-io.h (__gl_setmode): Put _GL_UNUSED before, not after, the
declaration.
* lib/c-stack.c (null_action, segv_handler, overflow_handler,
c_stack_action): Likewise.
* lib/chown.c (chown): Likewise.
* lib/clean-temp-simple.c (cleanup_action): Likewise.
* lib/fts.c (dirent_inode_sort_may_be_useful, leaf_optimization,
fts_set): Likewise.
* lib/getgroups.c (getgroups): Likewise.
* lib/getopt.c (_getopt_initialize): Likewise.
* lib/getugroups.c (getugroups): Likewise.
* lib/localename.c (gl_locale_name_thread_unsafe, gl_locale_name_thread,
gl_locale_name_posix, gl_locale_name_environ): Likewise.
* lib/mkdir.c (rpl_mkdir): Likewise.
* lib/mkfifo.c (mkfifo): Likewise.
* lib/mkfifoat.c (mkfifoat): Likewise.
* lib/mknod.c (mknod): Likewise.
* lib/mknodat.c (mknodat): Likewise.
* lib/mountlist.c (me_remote): Likewise.
* lib/openpty.c (openpty): Likewise.
* lib/parse-datetime.y (yyerror): Likewise.
* lib/passfd.c (sendfd, recvfd): Likewise.
* lib/pthread-cond.c (pthread_condattr_destroy, pthread_cond_init,
pthread_cond_wait, pthread_cond_timedwait, pthread_cond_signal,
pthread_cond_broadcast, pthread_cond_destroy): Likewise.
* lib/pthread-mutex.c (pthread_mutexattr_destroy, pthread_mutex_init,
pthread_mutex_lock, pthread_mutex_trylock, pthread_mutex_timedlock,
pthread_mutex_unlock, pthread_mutex_destroy): Likewise.
* lib/pthread-rwlock.c (pthread_rwlockattr_destroy, pthread_rwlock_init,
pthread_rwlock_timedrdlock, pthread_rwlock_timedwrlock): Likewise.
* lib/pthread-spin.c (pthread_spin_init, pthread_spin_lock,
pthread_spin_trylock, pthread_spin_unlock, pthread_spin_destroy):
Likewise.
* lib/pthread-thread.c (pthread_attr_destroy): Likewise.
* lib/readlink.c (readlink): Likewise.
* lib/rename.c (rpl_rename): Likewise.
* lib/set-permissions.c (set_permissions): Likewise.
* lib/sockets.c (gl_sockets_startup): Likewise.
* lib/stat-time.h (get_stat_birthtime_ns, get_stat_birthtime,
stat_time_normalize): Likewise.
* lib/strptime.c (__strptime_internal): Likewise.
* lib/strtod.c (LDEXP): Likewise.
* lib/symlink.c (symlink): Likewise.
* lib/symlinkat.c (symlinkat): Likewise.
* lib/tempname.c (try_dir, try_nocreate): Likewise.
* lib/textstyle.in.h (styled_ostream_begin_use_class,
styled_ostream_end_use_class, styled_ostream_get_hyperlink_ref,
styled_ostream_get_hyperlink_id, styled_ostream_set_hyperlink,
styled_ostream_flush_to_current_style, fd_ostream_create,
term_ostream_get_color, term_ostream_set_color,
term_ostream_get_bgcolor, term_ostream_set_bgcolor,
term_ostream_get_weight, term_ostream_set_weight,
term_ostream_get_posture, term_ostream_set_posture,
term_ostream_get_underline, term_ostream_set_underline,
term_ostream_get_hyperlink_ref, term_ostream_get_hyperlink_id,
term_ostream_set_hyperlink, term_ostream_create,
term_styled_ostream_create, html_styled_ostream_create,
handle_color_option, handle_style_option, style_file_prepare,
styled_ostream_create, libtextstyle_set_failure_exit_code): Likewise.
* lib/unicodeio.c (exit_failure_callback, fallback_failure_callback):
Likewise.
* lib/wait-process.c (cleanup_slaves_action): Likewise.
* tests/signature.h (SIGNATURE_CHECK2): Likewise.
* tests/test-areadlink.c (do_areadlink): Likewise.
* tests/test-areadlinkat.c (do_areadlinkat): Likewise.
* tests/test-ceilf-ieee.c (main): Likewise.
* tests/test-ceilf1.c (main): Likewise.
* tests/test-dirent.c (dir): Likewise.
* tests/test-fchownat.c (main): Likewise.
* tests/test-fdopendir.c (main): Likewise.
* tests/test-filenamecat.c (main): Likewise.
* tests/test-floor1.c (main): Likewise.
* tests/test-floorf-ieee.c (main): Likewise.
* tests/test-floorf1.c (main): Likewise.
* tests/test-fseeko.c (main): Likewise.
* tests/test-fstatat.c (main): Likewise.
* tests/test-ftello.c (main): Likewise.
* tests/test-getdomainname.c (main): Likewise.
* tests/test-getgroups.c (main): Likewise.
* tests/test-gethostname.c (main): Likewise.
* tests/test-math-c++.cc (OVERLOADED_CHECK): Likewise.
* tests/test-mkdirat.c (main): Likewise.
* tests/test-openat.c (main): Likewise.
* tests/test-parse-datetime.c (main): Likewise.
* tests/test-quotearg-simple.c (main): Likewise.
* tests/test-quotearg.c (main): Likewise.
* tests/test-sethostname2.c (main): Likewise.
* tests/test-unlinkat.c (main): Likewise.
* tests/test-version-etc.c (main): Likewise.
* tests/test-xalloc-die.c (main): Likewise.
* tests/test-xfprintf-posix.c (main): Likewise.
* tests/test-xprintf-posix.c (main): Likewise.
* tests/test-xvasprintf.c (main): Likewise.

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/test-floorf-ieee.c b/tests/test-floorf-ieee.c
index 2cf8d91743..3d261ed306 100644
--- a/tests/test-floorf-ieee.c
+++ b/tests/test-floorf-ieee.c
@@ -36,7 +36,7 @@ dummy (float f)
 }
 
 int
-main (int argc, char **argv _GL_UNUSED)
+main (int argc, _GL_UNUSED char **argv)
 {
   float (*my_floorf) (float) = argc ? floorf : dummy;