An empty argument list means "unspecified arguments", and not
"no arguments" like it does in C++. If an implementer of Mutter
plugins uses gcc -Wold-style-definition, as configured by
AX_COMPILER_FLAGS_CFLAGS, they will get warnings about this.
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Reviewed-by: Florian Müllner <fmuellner@gnome.org>
Bug: https://bugzilla.gnome.org/show_bug.cgi?id=769971