component/qemu-kvm: add missing extends

Now that component/glib/buildout.cfg is no longer included by pkgconfig,
qemu no longer build with:

    While:
	Installing.
	Getting section template.
	Initializing section template.
	Getting section template-nbd.
	Initializing section template-nbd.
	Getting section kvm.
	Initializing section kvm.
	Getting option kvm:configure-options.
	Getting section glib.
	Error: The referenced section, 'glib', was not defined.

Also explictly add pcre to prevent same problem later.