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The first commit avoids printing a warning on macOS whenever a window containing no actions is closed. See https://discourse.gnome.org/t/gtkmenubutton-not-working-on-macos/15177. That happens specifically on macOS because the only user of gtk_action_muxer_get_group() is gtkapplication-quartz.c

The second commit fixes compilation on macOS due to a name clash with the wait() function from <sys/wait.h>