[deadcode] keep intermediate files around on failure
[deadcode] keep intermediate files around on failure

Summary:
The are already ignored by git and can be useful to 1) debug when the
deadcode Makefile has a bug, and 2) help incremental analysis.

Reviewed By: ngorogiannis

Differential Revision: D21277538

fbshipit-source-id: dc6394ed7

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