In case of:

• CGAL branch build (top directory is the root of CGAL)
• maybe if the top directory is a sub-directory of CGAL (CGAL*/*/*/)

then CGAL_DEV_MODE default value should be ON.

Then, CMake could display a warning for user telling about CGAL_DEV_MODE being ON and how to set it OFF.

Cc: @sloriot @afabri