variable_requires
-----------------

Disallowed since version 3.0.  See CMake Policy :policy:`CMP0035`.

Use the :command:`if` command instead.

Assert satisfaction of an option's required variables.

::

  variable_requires(TEST_VARIABLE RESULT_VARIABLE
                    REQUIRED_VARIABLE1
                    REQUIRED_VARIABLE2 ...)

The first argument (``TEST_VARIABLE``) is the name of the variable to be
tested, if that variable is false nothing else is done.  If
``TEST_VARIABLE`` is true, then the next argument (``RESULT_VARIABLE``)
is a variable that is set to true if all the required variables are set.
The rest of the arguments are variables that must be true or not set
to ``NOTFOUND`` to avoid an error.  If any are not true, an error is
reported.