tools/flask: add FLASK policy to build

This patch enables the compilation of the FLASK policy as part of the
tools build if the needed prerequisites are present.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

config/Tools.mk.in

@@ -46,6 +46,7 @@ GIT_HTTP            := @githttp@
 XENSTAT_XENTOP      := @monitors@
 LIBXENAPI_BINDINGS  := @xenapi@
 OCAML_TOOLS         := @ocamltools@
+FLASK_POLICY        := @xsmpolicy@
 CONFIG_MINITERM     := @miniterm@
 CONFIG_LOMOUNT      := @lomount@
 CONFIG_OVMF         := @ovmf@