missing Makefile targets to rebuild `pbuilder`

[udance4ever]

I notice that the pbuilder executable doesn’t get rebuilt when source code changes.

This happened to me twice:

1. I made some local changes to graph_exec.c and it didn’t rebuild
2. I pulled new commits and pbuilder wasn’t rebuilt

I tried to see if I could figure it out in the Makefile but I’m not very familiar with how automake works.

It seems like there might be a missing dependency ongraph_exec.c?

This is low priority as the workaround is straight forward:

rm src/pbuilder

[paguilar]

The Makefile nor the python script were intended to detect if the source code changed and rebuild itself, but it's a good idea, so I'll add it to the whislist. Thank you.