[make] clean more
[make] clean more

Summary:
Keep track of generated files better and make sure we nuke them on `make clean`.

Also get rid of a few unused variables in infer/src/Makefile.

Reviewed By: sblackshear

Differential Revision: D5754553

fbshipit-source-id: b5fca41

jvillard/infer,jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer,facebook/infer,jvillard/infer,jvillard/infer,jvillard/infer,facebook/infer,facebook/infer