[make] run jbuilder when files in infer/src/ change
[make] run jbuilder when files in infer/src/ change

Summary:
Without it `make` will not rebuild infer when "infer/src/infer.ml" changes
(since D7381842 moved it out of backend/).

Reviewed By: mbouaziz

Differential Revision: D7443275

fbshipit-source-id: 33ea10b

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