src: don't statically link code that's already in libvirt.so

src: don't statically link code that's already in libvirt.so

Various binaries are statically linking to libvirt_util.la and
other intermediate libraries we build. These intermediate libs
all get built into the main libvirt.so shared library eventually,
so we can dynamically link to that instead and reduce the on disk
footprint.

In libvirt-daemon RPM:

            virtlockd: 1.6 MB -> 153 KB
             virtlogd: 1.6 MB -> 157 KB
     libvirt_iohelper: 937 KB -> 23 KB

In libvirt-daemon-driver-network RPM:

 libvirt_leaseshelper: 940 KB -> 26 KB

In libvirt-daemon-driver-storage-core RPM:

   libvirt_parthelper: 926 KB -> 21 KB

IOW, about 5.6 MB total space saving in a build done on Fedora 30
x86_64 architecture.

Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>