otherwise it installs an unused /usr/bin/luajit ....
-0
--- a/cmake/luajit.cmake
+++ b/cmake/luajit.cmake
@@ -6,5 +6,5 @@
   ${LUAJIT_DIR}/src
   ${CMAKE_CURRENT_BINARY_DIR}/lib/luajit-cmake
 )
-add_subdirectory("lib/luajit-cmake")
+add_subdirectory("lib/luajit-cmake" EXCLUDE_FROM_ALL)
 set(LUAJIT_LIBRARIES "libluajit")