Commit 448c03b3cb ("tools/xenstore: try to get minimum thread
stack size for watch thread") added a dependency to libdl to
libxenstore.
Add the needed flags to LDLIBS_libxenstore and the pkg-config file of
libxenstore.
Fixes: 448c03b3cb
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>