[docs] Update CMake cross compiling guide link.

[oToToT]

Summary

The CMake community Wiki has been moved to the Kitware GitLab Instance.
Also, the original anchor for Information how to set up various cross compiling toolchains section might not work as expected. The original content is now being collapsed, so browser won't navigate to the right section directly.

Hence, I think it might be better to provide the section name instead of this section with link to help readers find the right section by themselves.

[oToToT]

kindly ping

[void]

One small nit, otherwise good.

llvm/docs/CMake.rst

740

Please add a "the". I.e.:

Go directly to the ``Information ...

[oToToT]

add 'the' before section name

llvm/docs/CMake.rst

.. code-block:: console
   $ make check-all
 
 On Visual Studio, you may run tests by building the project "check-all".
 For more information about testing, see the :doc:`TestingGuide`.
 
 Cross compiling
 ===============
 
-See `this wiki page <http://www.vtk.org/Wiki/CMake_Cross_Compiling>`_ for
+See `this wiki page <https://gitlab.kitware.com/cmake/community/wikis/doc/cmake/CrossCompiling>`_ for
 generic instructions on how to cross-compile with CMake. It goes into detailed
 explanations and may seem daunting, but it is not. On the wiki page there are
-several examples including toolchain files. Go directly to `this section
-<http://www.vtk.org/Wiki/CMake_Cross_Compiling#Information_how_to_set_up_various_cross_compiling_toolchains>`_
+several examples including toolchain files. Go directly to the
+``Information how to set up various cross compiling toolchains`` section
 for a quick solution.
 
 Also see the `LLVM-specific variables`_ section for variables used when
 cross-compiling.
 
 Embedding LLVM in your project
 ==============================