* remove unnecessary include
* cmake: use pkg_get_variable
We can find wayland-scanner executable and wayland-protocols dir by
taking advantage of this function, so no need to use find_program or
manually call pkgconf executable.
* cmake: remove explicit rdynamic option
CMAKE_ENABLE_EXPORTS=ON already implies rdynamic so it's redundant to
set the latter explicitly.
Also, CMAKE_ENABLE_EXPORTS is superseded by
CMAKE_EXECUTABLE_ENABLE_EXPORTS in cmake 3.27.
* cmake: make xcb-errors dep optional
xcb-errors is being used in wlroots, where it's optional. So make it
optional in hyprland as well
