see https://github.com/GNOME/gnome-power-manager/commit/7568769f for a reference, though this is not a 1:1 copy

Add per-target CFLAGS variables to applet Makefiles to fix build errors
when objects are created with and without libtool.

Fixes #416

Properly anchor the popup menu to the applet widget to fix the menu
appearing in the center of the screen under Wayland.

This enables Wayland compatibility. Out-of-process applets use
GtkPlug/GtkSocket which is X11-specific and doesn't work in Wayland
sessions.

The default build remains out-of-process for backwards compatibility.

This applet allows the user to set the active power profile
(power-saver, balanced, performance). It's compatible with the
power-profiles-daemon and tuned, which are the same DBUS interfaces that
GNOME relies on for power profiles.

Also save brightness config changes when running on battery.
To do that, calculate backlight dim factor and ac brightness factor from
master percentage value so that ac factor is only changed if brightness
is further increased when battery dim factor is already zero.
This behaviour seems less random to me than only saving changes when
running on AC.

Add power manager switch to completely disable keyboard backlight
brightness control by GPM. This goes together with reverting the patch
that allows to disable keyboard backlight control via
kbd-backlight-battery-reduce.