oox: try to fix incremental build

The problem was that the input of the generated
vmlexport-shape-types.cxx got changed, but it was only built when
building from scratch. Fix this by depending on the makefile as well.

(cherry picked from commit b916fc4840ba67ef30e45ea735408237a3422b56)
Signed-off-by: Michael Stahl <mstahl@redhat.com>

Conflicts:
	oox/CustomTarget_generated.mk

Change-Id: Ia2d7f059aae2f5819bb8a1329fefa74c56660607