build: introduce and export XEN_LIB_DIR

This variable defaults to /var/lib/xen. It will be used to substitute
various hard-coded paths in tools.

The new variable points to $localstatedir/lib/xen, which defaults to
/var/lib/xen, so there is no change in default configuration.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

configure

@@ -603,6 +603,7 @@ XEN_CONFIG_DIR
 INITD_DIR
 CONFIG_DIR
 SHAREDIR
+XEN_LIB_DIR
 XEN_LIB_STORED
 XEN_LOG_DIR
 XEN_RUN_DIR
@@ -1980,6 +1981,9 @@ XEN_LOG_DIR=$localstatedir/log/xen
 XEN_LIB_STORED=$localstatedir/lib/xenstored
 
 
+XEN_LIB_DIR=$localstatedir/lib/xen
+
+
 SHAREDIR=$prefix/share