stubdom: fix "make build"

stubdom: fix "make build"

Cross compiling libxc requires some symlinks to exist.

Note that make -C tools/include requires running tools/configure. But at
least now the error message is much better than just a "file not found"
error.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jakcson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>