Add Makefile to rebuild targets for generated files

Add Makefile to rebuild targets for generated files

If you rerun ./configure with a different option (such as
--sysconf=foo), the changed Makefile needs to trigger a rebuild of the
generated files. Otherwise, the first generated version of the file is
always newer than its *.in counterpart and a rebuild won't be triggered
on subsequent ./configure runs.

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>