Just like we allow users overriding path to bridge-helper
detected at compile time we can allow them to override path to
qemu-pr-helper.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>
LIBVIRT_ARG_WITH_ALT is more generic than LIBVIRT_ARG_WITH, which
is tailored at switching features on and off.
Rename the macros according to their intended purpose, and add
some documentation to help developers pick between the two.
