Not possible to add variables to Makefile with flow API

[nicorum]

Variables added with add_var() to the tools EdaCommands object are not transfered to the flows EdaCommands object.
Since no official tool with flow api currently uses this, I wonder if this is an oversight or intentional behavior to not bloat the Makefile too much.

Could be fixed with a one liner, by adding:
self.commands.vars += node.inst.commands.vars
to the end of the configure_tools(self, graph) function in the edaflow.py