libmetalink: Fix source URL and add makedepends.
libmetalink: Fix source URL and add makedepends.

Source URL was getting a 404.  Also add libxml2-devel as a makedepends.

mati865/MSYS2-packages,mati865/MSYS2-packages,JPeterMugaas/MSYS2-packages,mati865/MSYS2-packages,Alexpux/MSYS2-packages,Alexpux/MSYS2-packages,juergenpf/MSYS2-packages,atom2013/MSYS2-packages,atom2013/MSYS2-packages,JPeterMugaas/MSYS2-packages,Alexpux/MSYS2-packages,Alexpux/MSYS2-packages,juergenpf/MSYS2-packages,waterlan/MSYS2-packages,waterlan/MSYS2-packages,atom2013/MSYS2-packages,waterlan/MSYS2-packages,juergenpf/MSYS2-packages,waterlan/MSYS2-packages,mati865/MSYS2-packages,juergenpf/MSYS2-packages,atom2013/MSYS2-packages,JPeterMugaas/MSYS2-packages,JPeterMugaas/MSYS2-packages,juergenpf/MSYS2-packages