Check for kxc & fxc support in libxc >= 5.1

Description

The recent versions of the libxc are not compiled with kxc and lxc support by default. We check the kxc support of the library in the configuration script and set HAVE_LIBXC_KXC if the library supports it. xc_get_kxc() subroutine will fail with a fatal message if it's called without the kxc support in the linked libxc. The failing tests of #465 (closed) are also being adapted to this change.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.

Closes #465 (closed)