Allow to add dependencies to auto-defined target Makefile.tcl

[ethouris]

The automatically generated target Makefile.tcl is normally dependent only on the Silverball file only.
There's a need to put additional dependencies that result:

• from the already existing support commands - such as ag-maf or ag-require
• by user's explicit declaration, should they use custom extensions

This should effectively add other files to be dependencies on Makefile.tcl so that changes there will trigger build regeneration.