Commit 596fc3e389 introduced the ability to detect xenstore
using pkg-config for systems with Xen 4.9, but accidentally broke
detection for all other systems. Fix the logic so that it works
in all cases.
Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Since Xen 4.9 a pkgconfig file exists to gather info about building
against libxenstore.so. Use it if available.
Signed-off-by: Olaf Hering <olaf@aepfle.de>
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.
