Revert "cmake: Remove redundant include_directories()"

This reverts commit 9b1ea1c7.

This breaks compilation; apparently the include is not implicit and is
thus needed after all.

CMakeLists.txt

@@ -358,6 +358,8 @@ if (KWIN_BUILD_XRENDER_COMPOSITING)
     set(KWIN_HAVE_XRENDER_COMPOSITING 1)
 endif()
 
+include_directories(${XKB_INCLUDE_DIR})
+
 set(HAVE_EPOXY_GLX ${epoxy_HAS_GLX})
 
 # for things that are also used by kwin libraries

[Vlad Zahorodnii]

include_directories() is not the solution. It's rather odd that I don't have any compilation errors on Arch Linux.