The problem is that CPAN does not (and could not be expected to) be able to reason: "Ah! libxml is missing and I am about to install XML::LibXML. I'd better install libxml first."

What you can do is reflect the C library with a Perl distribution (e.g. Alien-wxWidgets). During installation, the distro checks if the necessary C library is installed. If not, the distro either fails to install itself or it installs the C library.

XML::LibXML
   -> depends on Alien::LibXML (i.e. libxml2)

Alien::LibXML
   -> Installs libxml2 as part of its installation
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