libxml2-dev package needed to compile llvm-project via babs.sh on Ubuntu 24.04

[phdonnelly]

Looks like in llvm-project the file WindowsManifestMerger.cpp references libxml/xmlreader.h provided by the libxml2-dev package in ubuntu.

That wasn't installed by default on a fresh 24.04 install. Installing it manually fixed the problem, but it should probably get added to the install_deps.sh script