[libvirt] make failure in HEAD

[Dave Allan <dallan redhat com>]

I'm seeing:

/usr/bin/ld: libvirt_lxc-domain_conf.o: undefined reference
to symbol 'log2@@GLIBC_2.2.5'

when building the git HEAD just now.

It appears to be the result of:

aa14709a src/conf/domain_conf.c (Matthias Bolte     2011-07-11
19:29:09 +0200  5868)
virDomainVirtTypeToString(log2(expectedVirtTypes)));

I don't have time to look into it, but thought I should mention it.

Dave