mark_as_advanced
----------------

Mark cmake cached variables as advanced.

::

  mark_as_advanced([CLEAR|FORCE] VAR [VAR2 ...])

Mark the named cached variables as advanced.  An advanced variable
will not be displayed in any of the cmake GUIs unless the show
advanced option is on.  If CLEAR is the first argument advanced
variables are changed back to unadvanced.  If FORCE is the first
argument, then the variable is made advanced.  If neither FORCE nor
CLEAR is specified, new values will be marked as advanced, but if the
variable already has an advanced/non-advanced state, it will not be
changed.

It does nothing in script mode.
