Prefer bundled wlroots headers to system ones (hyprwm#2204)

In the case that the prefix is `/usr`, system wlroots headers installed in `/usr/include/wlr` will be preferred over those bundled by hyprland as `-I` directories are searched [from left to right](https://gcc.gnu.org/onlinedocs/cpp/Search-Path.html), which is not great since the system wlroots headers might not be compatible with hyprland. Fix the order of cflags so bundled wlroots headers will be preferred over system ones.

hyprland.pc.in

@@ -5,4 +5,4 @@ Name: Hyprland
 URL: https://github.com/hyprwm/Hyprland
 Description: Hyprland header files
 Version: @HYPRLAND_VERSION@
-Cflags: -I"${includedir}" -I"${includedir}/hyprland/protocols" -I"${includedir}/hyprland/wlroots"
+Cflags: -I"${includedir}/hyprland/protocols" -I"${includedir}/hyprland/wlroots" -I"${includedir}"